They could have larger combustion chambers, lowering your compression. What are the casting numbers? Are you sure it is a 260?

 

I'm 99% sure that it is a 260.

 

The only 302 head that wouldn't be too bad is the 302-4V from '68. Everything else is dropping your CR a lot.

 

I just checked and they are the 4V heads.

 

If they're still bolted to engine block what are the date codes below valve cover? on bottom they would have casting #'s...

 

If I'm reading them right they are 7629 and 7HI

 

#LETTER## format so
Looks like July 29, 1967 (G=July) and Aug. 1, 1967 (H=Aug.)

 

That's good to know. That "76" must have been 7G. The blood rushes to my brain when I'm standing on my head to read read those #'s.

 

If they are, indeed, '68 "J" code 4V heads, the advantage is that they have the same 53.5cc combustion chamber size as the original 260-2V head and a larger 1.78" intake valve, instead of the 1.67" intake. The only disadvantage I can think of is that they most likely have a Thermactor "bump" cast in although it may or may not be drilled. With this restriction removed and some gentle port smoothing and matching done it will flow just as good or better than a budget aluminum head.