Yeah i ran into this last year. I swapped my intake manifold for an Edelbrock performer unit and the new Vacuum tree location fouled on the large HEI cap. After research i went and looked for the XD falcon cap and it took many shops to find one as well as the rotor. Ended up getting a cap from Speed Parts in Hallam (obsolete stock still on hand) and the matching rotor from over in Bayswater (Vic) somewhere.