Pushbutton to 4 speed 64 Dart

Anyone swapped a swapped out a pushbutton trans on a 64 Dart for a 4 speed?
I have the PB that keeps giving me issues. Picking up a donor with a 4 speed.
How difficult a swap is this?
Thanks in advance for any advice/ lessons learned.
what's a PB?
as for the tunnel, aren't they all the same?
If so, I used an aluminum bell housing out of a 70 340 Cuda. I think the only mod to the BH was that I sawed off some unnecessary ear on the BH, and I'm not sure that I didn't do that just for header clearance.