The older head doesn't accept the fuel injectors. Intake manifold is "different". It had DuraSpark, IIRC.
Clifford Performance in California is among the leaders in performance products for straight 6s. They offer a good 4-bbl. intake, a "split" header and numerous other "goodies" that only fit the 6. Holley offers smaller 4-bbl. carbs, down to 390 CFM. One of those 500 Edelbrocks might even be a good "match" for the 6. MSD and Mallory have distributors.
Comp and Crower offer some nice grinds. If your budget can stand it, rollers are available. The "stock" head can be made to flow pretty well, using 1.94" intakes and 1.6" exhausts. Screw-in studs are important. They're installed in the same manner as those in the small V8s. Isky offers an "adjustable" guideplate that will also fit fine.
If you wanna get "silly", there are a few old Cleveland heads still floating around for them. I don't recall who, maybe Roush, but someone cut up Cleveland 4-bbl. heads and welded them back together to fit the 6. I saw one in '76 in a '63 Falcon going 10.60s. It was a RACE car, but it illustrates the power potential.
IMO, the Ford "big" 6 is a good power plant. It can be "pumped up" successfully. It is, however, limited in high-end performance. While it can rev like a V8, it just doesn't "pull" up high like a V8. For a "truck", it's excellent. For a "toy truck", it's fun but don't expect to kill "giants". In truth, a mid-sized V8 (like a 351W) would be much more fun and a little "easier" to deal with. So, if you REALLY like the 6, go for it. Otherwise, just drive it, enjoy it, and collect all the stuff you need to upgrade to the V8.
FWIW
Jim