Kelly I think the $8k price is mostly in the working pumps, which are fiddly and very old. The copper(?!) bellows at the center of them are interesting. There are dozens of other parts in there too.
You're right about the manifolds though. If I were a better man I'd make wax copies of my bogus ones and then sand-cast them out of aluminum and tap them for functionality. Heck, maybe it'll even happen.
You're probably right about the pumps themselves too. There appears to be a lot of P-car pricing at work here.