WIth a 408 or bigger motor, you will need to probably source a 4 barrel throttle body if you insist on going that route. Any stock GM unit won't cut the mustard. The biggest they offered was 670CFM on the 454, which Holley robbed for the first Pro-Jection kits. That throttle body is what I have on the W350 and even a mostly stock 360 will test the limits of that. It's already at the biggest injector made for that application and rated for 275hp, so nowhere to go besides adding more injectors. Also, the GM computer will have no provisions for overdrive control. I can't speak for some of the aftermarket or unlocked ones out there.

To save budget on the SB build, I would scavenge a setup out of a 94-96 Dakota. It will have all the wiring you need. Megasquirt 2 or 3 will more than handle what you are looking for. I built mine off the Pro-jection harness and added what I needed to make it work. At some point I will probably go to a magnum top end and 8 injectors in batch fire configuration, unless I end up going with a Cummins... There can be some issues with the low impedance injectors which require additional equipment.

I can't complain...for a 1 ton truck with 4.10 gears and overdrive,pulling the 2 big mountain passes it averages between 16-18 on the highway. I've yet to get it on flat land to see what it will do.