I have seen your other posts on this conversion.
You want to change everything on the '65, EXCEPT the exterior sheet metal and the gas cap.
With all the systems that you want to add to the '65 frame, you will be re-engineering and fabricating till the end of the next decade. Unless you are really good, you won't be able to make it as good as Chevy did.
Why not just find a late model and fit your '65 sheet metal to it. It may require some extensive sheet metal work, but that would be the only job.
On the new truck I would remove all the front sheet metal, bed and cut the cab away from the floor, firewall and dash. Leave the floor attached to the frame and firewall. You would have had to modify the '65 floor to get the ZF S6 under it anyway.
I don't think mating the late firewall up to a '65 cab would be that difficult, but the dash is about a foot deeper.
Tomy2tone01 extended the cab and doors on his AD and I am afraid something like that would be needed for what I had in mind.
As I said, a lot of body work, buy look at the options you get to just bolt back on.
