5.0s in everything but Mustangs (and MKVIIs) used the old 302 firing order; 1-5-4-2-6-3-7-8, 5.0 HOs used the 351W firing order; 1-3-7-2-6-5-4-8. Depending on which computer you use, it's to your advantage to run a matching firing order cam. You *can* use a Mustang computer with a non-HO cam, but idle may suffer a little due to fuel puddling. The intake manifolds just have to be matched upper to lower-that's really all that matters. The non-HO 5.0 passenger car intakes were a little different I think, but they can be ported just like the standard Mustang HO intake. The truck intakes OTOH, were extremely long runner and built for torque. There used to be a company that made box uppers for truck lowers and they flowed tons of air-especially on supercharged apps, but I doubt they're made new anymore...unless you're a fabricator, it's eBay for that particular setup. Otherwise, 5.0 intakes are readily available-and tons of folks part out their old combos with ported intakes and such all the time. But, depending on your expectations, you might wanna look into an aftermarket version anyway-like TFS, or Edelbrock.
If I had any other advice to offer though, I'd say ditch those E6 heads...they're only good for a boat anchor or door stop...crap for flow because of the shrouded intake valve. They can be made to flow decent, but the amount of work involved negates any positive outcomes-unless you're looking for a wheezing engine with no top end. At least look for some GT40s or GT40Ps, or go aluminum.
The electronics and harnesses are in several cars, but since most mods are focused on Mustangs, I'd recommend getting a good used harness from one if you can find one for a good price. The t-birds, trucks, and other vehicles wiring had slightly different pin-outs and the computers used different programming...
