I dug up an old thread in this forum on this with some good info:http://www.concoursmustang.com/forum/index.php?topic=4203.0
When I had to figure this out for our car to get it correct, I found the MustangTek site and Bob Manell's book as sources. What I found was that for '65 and '66 cars, there were two critical factors determining which 7-blade fan your car had:
Before 1/5/66, w/factory air: C6OE-C
Before 1/5/66, w/factory air & thermactor emissions: C6OE-A
After 1/5/66, w/factory air, w or w/o thermactor, C6OE-G
All of these 7-blade config's got fan clutches because of the A/C extra load on the engine. Thermactor a bit more (but negligible in some reading that I've done on this).
All should have also had a fan shroud and I believe a hot idle compensator spliced into the pcv hose to the carb spacer.
Hope this helps out somewhat.