Here is a Kit and explanation from
CPP. You can see that it is nothing more than two plates. Not much difference in the box mounting for 4wd.
I have made my own mounting plate for a 56 GMC 4X4 conversion and I also now have a 1960 GMC 4X4 with a previous owner installed box. Owner fabbed/mounted. Both use the Saginaw box. It really is not a major effort. Just involves mocking up the box, designing a plate and arrange the steering shaft hook up. Then find brackets for mounting the pump.
The difficult part is the pitman arm. My 1960 uses a welded (fabbed from two) arm. Once the box and plate are mocked up (NOT BOLTED UP OR WELDED), the search for a pitman are begins. If one is not found, make one.
There are "drop" pitman arms available and I think adjustable arms.
You can, of course, buy the CPP kit or equivalent from the aftermarket. I do not know if the pitmans available will fit. Maybe a member here has found a pitman for 60-66 4X4 or other.
I will post a pic of the 1960 if you decide to follow thru with this effort.
