Sorry, friend...I have not kept up on all the specifics of this problem you're having.
I recall that you're an avid enthusiast that isn't looking to set world records, you're just a guy that wants to have some fun.
It used to be that YEARS ago when these classics were just used cars, machine shops were in abundance. The cars today have engines that run so long, people just trade them in instead of replacing worn out engines.
For example, my 2007 Dodge truck has almost 400,000 miles on it and it is still running pretty good. By this point, many cars from the 60s would be on their 3rd engine. Leaded gas and oil technology didn't make for a real long lasting engine so there were a LOT of machine shops in business rebuilding engines. Even here in California, a place that some still call the "birthplace of the Hot Rod", it can be hard to find a machine shop. I'm sure that is why CRATE engines became popular.
Good luck.