OK I don't want to go through the trouble and expense of pulling heads to swap out for something that does exactly the same thing.

CC - same? 58cc?
intake port volume - same? 163cc?
exhaust port volume - same?
chamber shape same?
valve sizes Intake - 1.94 vs 1.84? Exhaust valve same? 1.50?

chamber shape same?

 

The 305=1.84 valve
L98 alum=1.94
both are 58cc

Alum is about 22lbs lighter /head

The L98 alum are superior, just they are more $

 

So other than intake valve size and weight, they're identical?

port shape? combustion chamber shape?

If that's it, it ain't worth swapping out heads.

 

The aluminum heads also don't have an exhaust crossover so your EGR system won't work AND the aluminum heads use the earlier style intake bolt pattern.

I have heard several people report that the ZZ4 versions of those heads have significant port/valve/valve seat improvements over the original assembly line corvette L-98 heads.

 

I was going to swap in the L98 alum in my 305 and I was hoping for about 30hp and 45lbs off the front end.

IMO, it's worth it for a 305, for anything bigger in cubic inches, not worth it.

 

https://www.thirdgen.org/forums/tbi/...-headflow.html

 

I think my numbers in my sig speak for them selves. I have a bone stock bottom end 305 with these heads, a mild cam, and ported stock intake parts with a bone stock chip. In my opinion these heads are the ideal setup for a 305.