1967 cab on 1973 frame vs. 1973 parts to 1967 frame

[oldcarfart]

Hello!
I am fairly new to the 67-72 truck series and need some opinions (oh no!). I have an early 1967 truck with the small back window and would like some input on this build. The truck will get bagged or dropped. I have the 1967 stepside, a 1969 stepside, a 1973 stepside and a 1970 stepside and will build one vehicle from the best parts in this group then sell off unused components later.

1. Will the 1967 body fit the 1973 frame so I can use the disc brakes, power steering, etc. already there.
or:
2. Dissect the 1973 frame and use the parts on the 1967 frame to upgrade.

3. Which rear suspension is easier to drop or bag, the coil rear (my assumption) or leaf springs.

any input greatly appriciated, Thanks in advance!!!!!!!!!!!!!