Researched the topic and found a very nive thread on it but one thing it didn't address was what type of material would be best for the bolts used to plug the injection holes? Something with the same rate of expansion to aluminum I would think. Brass maybe?

resuse the injector tubes themselves, but cap them off with some plumbing caps (surprisingly the same type threads)

works like a charm, and avoids the heat expansion issues.

That must be a Calif. only thing. My 76 had no air pump, egr, or cat as far as I know. When rebuilding engine no holes in head or signs of anything being plugged.

All 75/76 cars had air injection ports on the heads. If yours doesn't, the heads have been swapped.

not true my 75 1.8 has no holes or smog pump. did have a cat thought

I stand corrected, forgot about the 1.8L.

You could use those holes to put individual egt probes in and use the quad gauge that I posted a few minutes ago---would be too-cool to monitor all four cylinders at once!!!!