I agree with cletus66, that you should be able to find all the oem items for the engine swap. I don't know about the c6 swap. The drive shaft length may be different, linkage may be different, (if so you can install a cable shifter) also I am assuming that your F-250 is 2wd, if not then you will have a problem on the c6 tail shaft.
My truck that has a 385 engine in it is a 1977 F-150 4X4 that I race, I made all of the mounts.
I have a 89 that I bought to put a 460 in, but never went through with it, so keep us posted as how it goes.
A clear conscience is usually the sign of a bad memory.
1977 F-150 4X4 SWB
460 + ?
4.5 Bore X ?
and who cares,
if your winning your cheating, just ask the