wcbrowning, yes had to open up the floor pan, primarily to get the drive line angle correct and to get the engine back to it's original location. I used the original Z bar and clutch linkage with a new throw out bearing.
I did this about a year ago and had good intentions of posting it under Member Projects. Unfortunately I guess I got lazy and didn't totally complete the write up for the project so it never got posted. I do have lots of pictures and the write up is mostly complete. It covers a lot of the details regarding transmission mount, cross member placement, parking brake cable, etc. There was a few challenges that the kit from American Powertrain does not address. I could share with you if you're interested. I would guess 63.5 and 64 are probably very close.
My car is pretty much all street use and I am pleased with how it all works when I got it finished.