David,
I dont recall there being a difference.
Its been about 30 years since my last cab change on one of those style trucks.
Put a 65 chevy 20 series cab and nose on a 60 chevy apache 30 series tow truck for my buddies Dad.
Only thing I believe that was different was the location of the front cab mount bolts,they were narrower on the 65.
If you know what I mean,looking at the front floor supports there is what looks like a double step.
Inboard location was for 63 and newer,
Outboard location for 60-62 with the torsion bar suspension.
The Rubber Isolation Bushings were all the same though.
Regards....
