E550 seems a little much. They are very hard to find, but I don't know if I could justify that price point. I bought my G Rudolf Uebel, Reform-Boehm, for about $220. Granted, the bridge key is broken but that's a sub-$100 fix, placing it in the $350 maximum range.

I don't know much about these. I do know that they are pretty rare (at least in the US), and considered to be pretty good.

For your purposes, I doubt you could spend the $200 on a refurbishment (making it E750), and then still be able to sell for a profit. They're nice, but not THAT nice. 

Insert pics into thread and it'll work much better.

That's definitely an ABS plastic material. I'm not sure if the striations were meant to emulate wood grain or just a product of production, but it's definitely not metal.

That logo looks like its from the early 80s, I think.

I have a 1923 Buescher alto. Pretty much a museum piece. This soprano you found is a real gem. I sure hope grandson appreciates it.

Pics will be infinitely useful to determine age.

Don't see a problem with it. Jupiter clarinets aren't really commonly faked.

Wait, the barrel doesn't detach? Well that's definitely unique. Can't say I've heard of that before. I'm sure you've checked, but it could be stuck on?

I feel like you'd be better off just getting an entirely new clarinet. The odds of getting a perfect match on a Frankenstein'd clarinet is pretty minimal.

Not impossible, but you'd basically find yourself trying every joint you come across until you magically find one that fits just right. I don't know if there's any real advice I can give, other than just keep trying.