^ all of what @Sacto Mitch said. Every last word of it.
The least relevant bit of information is who splashed the body. In addition to all of the things mentioned above, there's the fact that Vintage ALSO did finish work on some guys' unfinished kits (of various manufacture). If it is titled and registered as a VW, who's "kit" (a term to rankle and rouse the rabble) ranks somewhere between "I wonder why they call it 'football'?" and "what if consciousness is an illusion?" in terms of relevance... but weighted pretty heavily towards the oblong ball.
The most important piece of the puzzle, who built the engine (and with what) is an open question with anything of unknown province. I've heard folks say that a car with such an engine should be fairly appraised as if it had no engine at all. That seems a touch excessive, but not by far.
Of late, there are cars with such engines selling for north of $35K on many venues. In that light, a 1641 for $3800 and purchased from a guy you can track down if anything goes sideways seems like a fair price of entry, at least to me. At that price, it'll be 99% stock inside - but there are still questions to ask: are the heads a matched set, or did one come from here, and another from there? Same deal with lifters: new or repurposed? At a minimum, the rings, bearings, lifters, and valve-springs should be new. If they aren't, walk away briskly. The VW hobby is populated by vendors who are thieves and/or charlatans, and more so out on our little branch of it.
If a new engine can't be trusted more than the old one, what have you really gained?
It'll take some time to learn who you can trust, and who you should run from. It may take a little bit - I've only been in it for 21 years, so I'm still learning. I'd say, "only trust yourself", but there are a thousand little things about these cars that will make trusting even yourself a fool's errand. They're riddles, wrapped in mysteries, inside enigmas. A light touch is a good thing, and every last part should be measured with a machinist's precision. The Sainted German Engineers were (evil) geniuses. I would assume you'll learn to admire and hate them, as any thinking person eventually will.
Thanks for posting pictures of your project(s) and of your shop. If you've got a home paint-booth, I'm going to assume you understand that in 2021 nothing comes cheaply or easily if it has wheels and an ICE. These cars certainly don't.
... and welcome to the madness.