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Performed a dry and wet compression test on my Six with a pronounced smoky exhaust issue at the request of my mechanic. To my knowledge, the engine is the 4 liter inline flathead six. Dry test - cylinders 1-4 read 110psi, #5 reads 105psi, and #6 reads 80psi. The wet test on 5 and 6 gave me 110psi and 90psi, respectively. I would like to acquire piston rings, but have learned from experience that not all retailers know which parts are correct for this engine. Additionally, I purchased replacement spark plugs based on what the owner's manual (I have one that looks original, came with the car, on the front cover stating "For cars beginning engine B-1501") spec'd - AC-103 or Champion Y-4. Auto Zone had a "match" for the 103's in Autolite brand, but they physically would not screw into the spark plug holes in the engine block. I discovered the plugs that are in use are Champion UY-6. Which leads me to wonder several things; why the mismatch, is the engine perhaps not the original one, and will my search for piston rings, and other items I intend to acquire for a tune-up or repair, be influenced by this mystery. The engine serial/ID number is 23870A. Who is a reputable retailer to acquire piston rings and other perhaps Packard-specific repair and tune-up items from? Any insight would be much appreciated.

Before buying pistons you would need to ascertain whether the engine has been rebuilt in the past and possibly rebored so that you know what size to get. As for source, I have Egge in my 1954 Patrician along with their pistons but those were put in decades ago.

Has this engine run much in recent times? That compression doesn't sound too bad. Is the gasoline fresh?

I agree compression is not that bad, but I suspect this is a clear indication of a valve issue not a ring issue. These engines required a valve job as a regular maintenance issue back in the day. This was due mostly to the quality of the gas available then. Egge can provide rings but it would be necessary to know what engine you have first. A routine valve job is not a big deal and you could do it yourself if you have some mechanical skills.

Thanks to all for the insights. The gas is fresh, on my third fill (non-ethanol premium with a lead-substitute added by me) since acquiring the car in July. Suspect the car sat for some time at Burnyzz's in Ocala, Florida, before it's transport to Oregon. My mechanic is willing to work on it, next year, (he is very good, and so is very much in demand) if parts are available (a task he has given to me), which seems to be the rub, as ID'ing the engine with any precision is proving difficult.

Perhaps I missed the post where you described it, but what's exactly wrong that you're trying to solve?

Running rough? Driving user load issue? Idle issue?

I think that the compression seems good for this engine. But if you still want to put in new rings, I have a set of Standard rings and a set of .02 oversize rings that I have no use for. These are new in their somewwhat beat up boxes from Packard. I would make you a good deal on these, so if you need them PM me.

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Kev (BigKev), without trying to replace the answer that only greybeard can give, I suspect he's worried about the smoke. He wrote at the beginning:

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Since we are talking about piston rings, it will probably be dark smoke.

I have encountered a number of old engines that smoked and ran poorly after being out of regular use for a period of time. Some of these responded very well to a tune up, oil change, and being driven a few hundred miles. Sticky valves and rings may free up, and driving the vehicle will provide an opportunity to accurately assess the condition of the various systems. Your engine may need an overhaul, or it may not.
The compression test results you report do not summarily condemn it, nor does the smoke, which may or may not be related to the rings. If it has reasonable oil pressure, does not overheat, and does not knock, driving the car isn't going to harm the engine. Exhaust smoke may be related to carburetor problems, air filter issues, sticky rings, or a failed vacuum booster diaphragm. Oil leaks may be aggravated by dirty or clogged crankcase vent devices. Excess fuel usually generates black smoke, while excess oil consumption usually causes a blueish smoke. Some water vapor emission is normal, and may make any smoke appear to be more dense than it actually is.I'd want to make sure the engine actually needs major work before tearing into it.