The early closed chamber heads
should be about 10cc smaller than the low-compression smoggers on your 74 engine. This will bump your compression up from a true 8/1 to a true 8.8. and your cylinder pressure up to 158psi@sea-level.
Even if your cam is stock, The Dcr on this new combination is just 7/1, so it should run on 87E10 at full timing.
If your cam is not stock, the later ICA will only reduce the pressure, reduce the Dcr, and that means for sure it will run on 87E10
If you are at higher than sealevel, the pressure will again be reduced.
All-in-all, I would rip the bad head off and have a look-see.
If your pistons are where they're supposed to be, down in the holes around .157 inch, you should be good to go, AND
if you find 020 steel headgaskets, that would be a good indicator that the engine is still original. If it was mine, I would install the thinnest headgaskets that I could find.