Long shot but stop in every mom and pop transmission shop to ask.
I traded a 65 727 for a '78 because the linkage was to complicated for me to make work in my 67
Didn't I post the inner dimensions for the M/Ts ?
The reusable valve gaskets will buy a little more hieght.
I didn't see the dimensions.. i don't have it together yet to measure though so.. wouldn't help :) I saw someone makes a 5/16th thick double cork gasket though so that's an option