[Offy 220]

Pech33,
Years ago [late 1970's] I did the same setup you are asking about in my '40 coupe - Ford 3 speed side shift transmission with the "truck open drive line." The stock Truck rear transmission mount is 8" on centers and the stock 1940 rear mount on a stock 1940 frame is 10" on centers.

I made these two "adapters" using the stock Ford donuts and machined collars to locate the adapters on the frame mount. You will have to purchase a GM PowerGuide rear yoke or after-market. The output spline on the truck shaft is the same spline as the PowerGuide yoke. As I said, I made this setup years ago so someone may have a better idea. Mac VanPelt's transmission booklet has information regarding this and part numbers you will need.