Youll need an engine harness, high pressure fuel pump, if its saddle tanks, price goes up, if its a rear gas tank setup you want, youll need a 87-91 gas tank so you can run an in-take High pressure pump.
if you run a 4l60e, 4l80e, or whatever, you'll need a trans controller.
If youre using a electronic auto from the said 5.3 truck, and your 77 is 4x4, you will also either
A. Need to convert the cable driven speedo to electric with an adapter.
B. Find an ultra rare 90 or 91 squarebody passenger drop np241 that uses VSS.
You will also need a 1990 or 1991 squarebody instrument cluster in conjunction with all of that.
If its just a 2wd truck, and youre running a 2wd 4l60e or 4l80e, then you'd just need the 90 or 91 cluster or get a aftermarket digital cluster that supports vss
If its JUST the 5.3, and youre keeping your 4 speed, or 3 speed auto, wont be extremely expensive id think.
I vote bbc as well tho
But thats my opinion, and this is the internet