One thing that troubles me about buying separate parts is, the parts specs and tolerances held today are not as they were, so when you mix old and new parts together they don't always fit the same. I have heard of problems replacing one gear or the fit and finish not quite as it should be.
Personally, if it were me and I was going to spend that kind of money, I would either get a whole new fresh build from a vendor with a guarantee, or replace all the parts with known NOS parts. There are NOS parts out there, you just need to look around.