Rod, I reckon restore the body to as per original, in original colour - don't stuff with it. Leave it DL7 to make it look cleaner.

THEN fit either a GenIV 6.0L and 4L65E box (don't bother with 6spd manual, too much butchering of the body). The standard TH400 shifter will operate the box and no tunnel mods are required. Even go to the trouuble of fitting a Black's Racks steering rack conversion so you can run all the GenIV accessories including A/C compressor in the original spot.

Go silly on the inside, do whatever you choose. Even just make it Caprice if that is what you want.