You’re welcome and I learned that after a lot of research trying to find the drain plug gasket for my 1965 Imperial. It’s probably Viton or its equivalent used on reproduction rubber parts that indicate they are ethanol-safe

On the Imperial and as a little aside, when I first got it to my Oregon shop and went to drain the tank, I found that the seal had entirely gone with the plug itself being held on by only a portion of a turn of the threads so lucky it was still there! The seal was an odd size and has to fit into a confined area so the OD and thickness was important too but someone on eBay was selling them in any size needed and happened to have what I wanted at a very reasonable price. I had already bought a new reproduction stainless tank but probably won’t need it.

Buna-N won’t last with ethanol but in this case there is very little contact so should be okay. Viton is what I generally look for but even that has different grades with more or less ethanol-resistance.

Interesting about the speaker control and it does look stock but I've never seen one in that location. On my 1951 through 1954 Packards, it is at the lower left side of the dash near the power antenna switch but it would make sense to put it near the radio which I believe is also where the antenna switch is on the 1955-1956 models.

The dash on the 1956 Patrician has a switch where the factory A/C control would be (to the left of the radio’s volume) but it has no A/C! Interesting and I wonder what it’s for. Maybe a rear defroster?

Although I’ve not yet tried it, I bought a fuel line cleaner from Eastwood for my 1951 Henney-Packard. If the tank is dirty, likely the lines are too and I don't want to simply blow them out with air!

Renu actually cuts the tank open to do the blasting, then welds it shut again. I had to have a similar process done on my 1965 Cadillac as reproductions are not available but in your case, you can buy a brand new tank so no need for all that. You could also try Hirsch’s tank sealer kit.

Are the ‘48-‘50 motors Trico? The one in my 1948 was not which was a surprise as I sent it off with many other later motors to be rebuilt by Trico themselves back in the day when they still did that sort of thing. They returned it untouched.

This is what the heat riser valve looks like from different angles (NOS).

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They merged in 1954? I understood that Packard BOUGHT Studebaker rather than merged with them. Perhaps a matter of semantics in this case but a purchase and a merger are two entirely different legal processes.

He nearly always makes mistakes - some quite serious - on makes and models with which I am familiar so I take what he says with a grain of salt on other makes and models where I am not overly familiar.