My one thought is those could go to the covers for thr bottom of the torque converter housing or the two little "wings" that link that to the bottom of the engine. A few of those bolts are really long. But they are installed after the ultramarine is attached to the engine.

I don't know all the details of the V-8's versus my straight-8. But the Packard V-8 as I understand it is of very conventional design, so tactics used for any other American V-8 of the 1950's and 1960's would apply as regards, say, exhaust manifold-to-exhaust-pipe bolts. Soaking them in Liquid Wrench, Sea Foam, or PB Blaster. Heat/Cold cylcles help too - heating them with a (acetylene or even hand-held propane) torch then quenching with something you can spray on them, like WD-40. On my straight-8 the exhaust manifold bolts were pretty rusty but did eventually come off. Another tactic (after the soaking and heat/cold cycles) is to use an "impact wrench" with a socket extension on it.

On the Straight-8 I found the easiest way to get the head off was to hit it on the side with a rubber mallet a few times, then there was/is a spot you can pry it up with a screwdriver without marring the machined surface. Don't know if such a spot exists on the V-8, but probably. After you get it to separate then progressively lift off by inserting, say, screwdriver blades and gradually work free. All that may not be as necessary on the V-8 since the head is not nearly as long.

I can lift off the Straight-8 flathead myself, which I cannot imagine isn't heavier than a single bank of the V-8 head, even though it does have lifters and valves in it. But again, Youtube videos of people working on big-block American V-8's would probably be a good thing to watch.

There is this one on Hemmings:

https://www.hemmings.com/classifieds/dealer/packard/400/1986124.html

and this one a little above your range but maybe you can talk them down:

https://www.hemmings.com/classifieds/cars-for-sale/packard/400/2539158.html

Which are readily available from multiple vendors

The 1953 Packards have the flathead straight-8 and either the overdrive or the standard Ultramatic, which are all relatively troublefree and work well, but it is all pre- mid-1950's tech, e.g. not a V-8 and not a 3-speed automatic, so not fast (though faster than you might think) and not something many mechanics know how to deal with (other than recommending an LS swap). 6-volt electrics though easy to swap over if you really want to. My 1953 actually handles very well for it's size and is a fun car to have, can drive it on the freeway fine, can keep up with modern traffic if I need to, and is no trouble to drive around town or even trips to San Francisco. Most people are not that enamored with the styling, but I think it looks pretty good. The 1951-52's have somewhat plainer styling than the 1953's and didn't have an available 4-barrel carb, so a bit slower, but otherwise the same comments apply.

The 1954 Packards often have the Gear-Start Ultramatic, which can be more troublesome, same comments otherwise as with the 1953's.

The 1955-56's came with the V-8 and 12-volt electrics, a more powerful if a rare engine, and various versions of the Twin-Ultramatic, which was an evolution of the Gear-Start, more sophisticated than the original Ultramatic but also troublesome and even more unusual, and still not as advanced as say, a 3-speed Torqueflite or (even better) a 700R4. It's somewhat common for folks to adapt a 700R4 or 4l60E transmission to one of these via the available Berendtsen adapter kit. Most people think the 1955-56 styling is very good.

Interiors as well as paint can be re-done with various levels of authenticity. Any local upholstery shop could re-do the seats and the carpet, but the only source for authentic or near-authentic upholstery that I know of is SMS in Oregon, who are kinda hard to deal with and have long lead times. I got my fabric from Lebaron-Bonney (now out of business), which was not quite authentic but of similar character. But if you don't require authenticity there is a lot of fabric out there that will do.

Note - from what I understand, if you have the Twin-Ultramatic rebuilt by someone who knows what they are doing, e.g. Ross or a few others, it works well, or even if someone just takes the time to go through the service bulletins and pay attention, it is not that complicated, but not easy to find someone.

All the engines except the 359" have the same bore, it's the stroke that changes. Ross I remember mentioned that the 288 might be the better performance engine, because it can be revved higher. The biggest performance improvement offered by Packard was the 4-barrel carburetor, offered beginning in '53 on the Cavalier and Patrician IIRC. Not sure if the manifold for the 2-barrel carburetor can be used for a 4-barrel carb, probably not.

The hydraulic lifters can be a pain if they are worn, solid lifters are probably better for your purposes.

Here is this nice chart that shows the various heads and how they can be interchanged amongst the engines for different compression ratios.

Packard 288/327/359 compression ratios for different heads

Reminds me of this:

"My Classic Tire" Holiday Special

From the product description. I and many others have used this stuff with great success:

1/4 In. x 60 In. copper/nickel/iron alloy tubing NiCopp is a nickel-copper alloy brake tubing that meets SAE standard J1047 and ISO 4038; meeting all international and U.S. requirements for brake tubing. This alloy is approximately 9.2% nickel, 1.4% iron, 0.8% manganese, and 88.6% copper. Under the ins system, this alloy is designated as ins C70600. NiCopp therefore has the strength and structural integrity of steel lines but with the added benefit of being much more corrosion resistant. NiCopp is also easier to bend and form than steel tubing. Nickel-copper, commonly referred to as 90-10 copper, has been used on several European vehicle brake systems since the 1970's, including: Volvo, Audi, Porsche, and Aston martin. NiCopp has been used on hydraulic/fluid transfer systems on vehicles where steel lines and tubing are commonly used. This includes brake, fuel and transmission systems. NiCopp is considered the super-premium brand in brake lines and should be considered where the under body of the vehicle is subjected to the harshest environments, where the longest life-span for lines is required, and/or where direct OEM replacement is desired. - NiCopp does not rust or corrode - dot approved for hydraulic brake systems - bends 58% easier than steel tubing - available in coils of 25 Ft., 50 Ft., and 100 Ft. - finished lines available for domestic & import - black oxide fittings 2X corrosion resistance. NiCopp lines and tubing meet the following specifications: SAEJ1047, ISO 4038, SAEJ1650, DIN 74234, BS2871

How about this? I used this it is great. It's in stock at the stores around here:

Autozone 1/4" NiCopp tubing x 60" with 7/16-24 Inverted Flare Thread Tube Nuts

Both Kanter:

https://www.kanter.com/packard/pac-sen.html

and Max Merrit

https://packardparts.com/contact-us/

have parts for those years in stock, though perhaps not the exact ones you need. Kanter in particular lists points and cap and rotor for those years, and Max Merrit has rebuildable starter cores and brush sets.

Will probably be able to help you. Best to give them a call (best) or write them.