I was looking in the Jeg's catalogue at intakes for my '87 Firebird engine. I know the intake bolt angles on the '87 and later heads are different than the the '86 and earlier.
What's the difference between aluminum and cast iron heads in the '87 and later style? Jeg's lists different part numbers for '87 and later aluminum and cast iron.
I thought it strange for there to be a difference late model heads just because they're made of different materials.

 

You left out one important word: insert between "later" and "heads", the word "iron".

The aluminum heads have the early-model bolt pattern; only the iron heads have the different one.

 

Oh, I get it now. The late model aluminum heads are basically identical to the early model heads, whereas late model iron heads changed the intake manifold bolt angle.
Thanks.

 

Aftermarket aluminum heads are generally available with either bolt angle.