[Dan in Pasadena]

These trucks came as both 3 AND 4 speeds for certain.

LS engines are the thing now and they make sense because they make great power and are economical on gas BUT you'll need a gas tank for fuel injection and of course you'll have to get a wiring harness made for the electronic fuel injection. Certainly worth doing but you posted you want "drop-in" simplicity.

My truck came with a warmed over 283 and I like it but it's got a weak cylinder and when I eventually deal with that the question will be whether to rebuild it, replace with crate 350(most likely) or search for a 5.3 LS engine.

EDIT: Just re-read my post above and saw that my "smart" phone posted "Pepe Boys" when I wrote Pep Boys. Apologies to my Latino brethren if anyone raises an eyebrow. I think it's kinda funny but others might not.