It might be a good idea to start a thread in the "Driveline" forum about getting the newer engine mated to the early drivetrain. There's an upgrade available to adapt a 3 or 4 speed synchronized transmission to your original torque tube rear end, but it would involve installing a different bellhousing and crossmember from a newer truck.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!