I suggest turning the engine over two full turns to make sure nothing is stuck. A 1" socket will do the job on the bolt on the front of the crankshaft. That is most easily reached from under the car.

Then don't even put a battery in it for preliminary investigations. Just jump it with good jumper cables from any convenient 12v car or tractor. I wouldn't even turn the key on. Run a hot wire over to the coil--if it doesn't spark as you connect it then either your points are open or are dirty. Use another hot wire to touch the small post on the starter solenoid to make it crank. These cars are not made out of cotton candy. Thus we move the parts cars around all the time. You will do well with an old lawn mower gas tank hanging on the drip rail to feed some fresh gas into the carb. Don't forget to plug the line coming from the fuel pump or you may get an unpleasant surprise if she does fire up.

I have the 145th 55 Constellation here and it has them spot welded to the molding. Later on they reworked the rubber gasket to take the place of those little troughs.

It's hard to discern engine sounds from a video, but here are two common things to look for.

Failing manifold gaskets will often make a very sharp sound under load as exhaust gas shoots out past them, and if there are leaks on the intake ports the idle will be very poor.

Noticeable ticking at idle means the valves need adjusting. I suggest you test the manifold vacuum and report back.

These are very simple engines and their problems are usually also simple.

Yes.

In the 48-54 era I have long viewed the 9 main engines as a marketing gambit. I can not tell them apart from a 5 main in driving and the 5 main still have a vast acreage of main bearing area compared to anything modern. Its not even remotely an issue.

I can only assume that the extra webs on the 9 main crank actually caused a loss of torsional rigidity as Packard equipped them with a huge whopper stomper vibration damper at the front where the 5 mains got a small one.

On the 56 cars the cushion does not lift off. You can take the back rest off after you remove the side shields and the whole bottom with tracks and motors and all unbolts from the floor.

The 257 was the first year of the 120 engine and had 6.5:1 compression. If you slapped that head on a 282 you would have (roughly)
282/257 x 6.5 = 7.1 CR.

As mentioned before, all 288-327-356-359heads are the same length, take the same head gasket etc. Those engines are roughly 1 1/2 inches longer than the 257 -282 family of engines.

High compression on a flathead turns into a two edged sword after about 8-something to one. Being a flathead, you begin to lose transfer area from the valves over to the cylinder and breathing can suffer. Sure, you can relieve the block, but then compression drops again.

You can mill .060 off the 282 head with no probs. Don't know what CR that will give you.

1936 has the regular 14 mm spark plugs, no? Any auto parts store will have kits for repairing damaged spark plug holes; you only need to know the length of thread.

Spark plugs need to tightened to about 20lb-ft. Of course this keeps them from blowing out, but also important it makes possible heat transfer out of the plug into the cylinder head. This prevents misfire and also pinging caused by the plug being a hot spot.

Any locations in your head that will not "hold" will need to be helicoiled. Get that taken care of before doing any more troubleshooting. It may also be that your coil is breaking down. It is past its normal service life by a factor of nine.

In 48 Packard standardized all their engines to a 3 1/2" bore. It had first appeared on the six (245), then the Super Eight (356) and lastly on the new 288 and 327. This means that the 288 and 327 and the 356 are all very close to the same length. In fact these all take the same head gasket and you can swap heads around for a compression ratio that you like.

If the 120 was sluggish there was something wrong with it. There are many old cars running around in a poor state of tune or just completely clapped out --the owners have unbelievably low expectations of how the cars should run.

A nice fresh 282 with OD will run along at 75+ all day if it needs to. Porting and relieving has a very good effect, as does a slightly warmer cam grind. Some careful attention to the head will get the CR closer to the 8:1 neighborhood.

I am not so much a 356 fan because of the weight that makes the car nose heavy, the hydraulic lifters, and generally more difficult to source parts. Needless to say any dual sidemounts have to go.

If you are changing to the longer engine, then for competition I would go with a 327 (which was a factory substitution after 356 production ceased). You are already up to 160 hp without lifting a finger and much more is readily available.