Welcome to the forum!
I'm not sure you'd need any kind of "kit"
You need a 16 gallon side tank, a cutting & welding rig and to bring your driveshaft to a shop to cut about 16" out and re-balance it
At least
I think a regular truck is 133" wb and a Flareside/short box is 117.
Fuel & brake lines are easy enough to shorten.
You could probably get away with making a loop in the electrical harness. 💡
Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.