No, I don't know if the current 3-speed is a Saginaw or a Muncie. I'll find out for sure in a week or two. (Why? I take possession of the car in a week or so.)

A Saginaw 4-speed? No. Everything I've read advises not for performance applications. While the Sprint may not over power a Saginaw 4, I'm not entirely sure I'll keep the OHC 6. I want improvements to the car to be future proof. A Saginaw 4 won't hold up to an LS...the likely transplant.

If I do change the engine I'm in no hurry. Everything else about the car needs to be upgraded before installing a healthy modern V8.