Forgot to mention, Walt is right on the Powerglide-350 swap. The aluminium case PG thru
1966 had a shorter output shaft with a course
spline. They also had a rear and a front pump which allowed push starts.
In 1967 the rear pump was dropped and the output
shaft was splined the same as the 350 TH. The
shaft was also a little longer.
If the trans is a 1968 the swap is pretty much a bolt in except for shift linkage and kick down
cable.
Once again my 2 cents worth
Gordy
