The aluminum heads are worth a bit of power compared to the iron heads, even with the B/D car cam. They also come factory with screw in studs rather than pressed in. The chambers on a LT1 aluminum head are 58cc and the cast iron about 66cc. The iron heads used a thinner head gasket than the aluminum heads, but the aluminum head guys use the iron head head gaskets for more compression. I would not waste my time with the iron heads. I put a pair of 200cc runner, 64cc aluminum heads on my L31 in my Express van and gained torque everywhere and was able to run 87 octane with a 9.6:1 compression ratio and 34* total timing at 2,400 rpm.