The con is your 518 transmission.

I wouldn't waste one second trying to make that turd work with a Gen 3.

Take the 545rfe or 8 speed that comes with the Gen 3 and never look back.

(Grab every inch of wire and computers from your donor vehicle while you are at it. )

I can't remember is your truck has the 318 or 360? If 318, maybe look at a 360 Magnum like "The Gas Tap" on Youtube has........