Engler had three castings for "I think" a Toyota or SP-2 sprint car head that had not had the manifold bolt holes drilled yet. The port spacing was almost identical to the P-7, so it was just a matter of drilling the P-7 bolt pattern and matching each base to the heads. The butterfly bodies are separate and could be bolted to different bases if needed. They (Sanborns)had three different sets of P-7's (Elliots, Davis's and one other, Arringtons, maybe)so that gave them flexibility if they decided to use a different head than the Elliots, since from what I understand, the intake ports are somewhat different on the three heads.