It uses mamiya press lenses, the focusing helicoid and shutter are in the lens.

What is the quality like for these lenses? This says the system was discontinued in the 1970s.

https://en.wikipedia.org/wiki/Mamiya_Press

I've seen a lot of Mamiya 645 and 67 systems but those were probably from the 1980's and 90's.

Ahh, I totally missed that detail. That makes the whole thing so much more feasible.