Join us on Facebook: Search for 'ConcoursMustang' Private group!https://www.facebook.com/groups/concoursmustang/Indiana SAAC Fall Classic , French Lick, IN Oct 11-12http://www.insaac.org/SAAC National-Sanctioned Concours Event
For one thing it is a different offset because its driven by different pulley. I think the theory of the larger pulley is that it requires less hp to turn a larger pulley
The rpm issue is moot, e.g. on a 390 they used two differnt diameter puleys for AC vs non-AC, so same RPM range as its the same engine. As an engineer I can't see why they would alter the pulley offset on the PS and make assmebly more complex, and the cost of more parts, and not just accomodate at the AC pump??? Very odd... but....Off to try to find a 6AA....