83-87 Ranger 7.5" diff is 1.5" wider then the stock Mits. I use one in mine and went with a 17x7" rim's with a 42mm back space and they fit fine. You can probably go with a Toyota 7.5" as well out of a P/U. Front have been converted to the 86-94 Toyota hub so it runs the 5 x 114.3 as well. there is a post about doing the front swap somewhere on the site. As for the swap just grab a 4.3/T5(700R4) out of a S-10 or a Safari Van, Unless you can fine the 3400/3500/3800 out of a Camaro or Firebird as the RWD engine mounts are expencive as hell or next to impossible to find.Headers are no real problem all you have to do is cut them up and modify them to dump where you need them. Not sure about the oil pan but someone else might know what to do to make them clear.

Welcome to the site and I hope you enjoy the truck.