A lot of confusing info in this thread.
1) you can swap valve bodies between the PB trans, and the 65 trans (as stated, the valve body must match the shifter).
2) You can swap the manual valve and detent from a PB trans into the 65 trans. You cannot put a 65 manual valve in a PB valve body. The PB valve body has a closed end where the valve goes, and the 65 manual valve is longer, then the 64 valve.
3) Crank pilot and input splines on the trans changed between 67 and 68.
67 down had a pilot dia of 1.550 and a spline count of 18
68 up non lockup had a pilot dia of 1.810 and a spline count of 27
4) to put a 67 or older trans to a 68 or newer engine, a adapter ring is required in the end of the crank, and the late flexplate. (slant six or small block).
5a) to put a 68 or newer trans to a 67 or older engine is harder. "Hybrid" converter with small pilot and 27 spline count. Hipo converter companies have been discontinuing this, and the ones that still do are pricey. Dacco converters still has this available in a stock stall speed configuration.
5b)Swap the early front section of the trans (input shaft, pump, etc) into the late trans, and use the early converter.
5c) use the late crank in the early engine,
5d) bore out the early crank pocket from 1.550 to 1.810, and use the early flex plate.
For performance converters, there is no problem getting them in either early (1.550 pilot and 18 spline), or late (1.810 pilot and 27 spline) it is just the "hybrids" that are the problem
I think I covered every thing