i want to put a rpm airgap manifold on a 87 later heads cast iron. but edlebrock only makes plan performer for 87+ heads.will a rpm airgap for 86 earlier head fit?

does anyone have experence with the power diference between performer and performer rpm.

with a 5000 redline will a rpm intake get me more power

and if the performer rpm for 86 doesnt fit do you guys think if i put a performer for 87 and a 1/2 inch spacer give me about the same results