Need some push button learnin

I'm hoping a few of you guys on here are some push button transmission gurus, because I have a few questions about and upcoming build.

I've got a long tail shaft cable shift 904 out of a 65 273 Belvedere, and a short tail shaft push button shift 904 out of a 64 Dart.

I am planning to, assuming it's possible, take the first two gears out of the slant 6 transmission and put them into the V8 transmission. I am also planning to convert the V8 transmission to short shaft using the Slant six output shaft and tail housing. I am also wanting to keep the push button shift, do I need to use the 1964 valve body? What other problems am I missing?

The whole point of this is because I am taking the slant 6 out and putting a V8 in.