Look on the door sticker for the transmission code.
I would assume C4 or AOD, but I'm beginning to forget, and I'm not so good with the lighter pickups.
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.