Hi Charlie
As I mentioned, the V8 will move the F15A OK but just won't accellerate quite as well - I use the word "accellerate" in a relative sense.
The gearboxes are identical throughout the range of Ford CMPs from 8 CWT to 60 CWT as are the Chevs, even the C60X with the GMC 270 uses the same 4 speed box as other Chevs.
As for drawings, how about this?
No complete set exists as far as is known, but if you have a look at my
page on the subject, as well as some of the
reference images you should have a reasonable idea of what to make.