I have a 67 Mustang Convertible which I am restoring. I am putting the 6 cyl engine back in it but the engine came out of a 68 Ford. The car has AC and power steering. I actually like the pully and bracket system on a 68 more than a 67. The question I have is the engine I got for the car came with a two groove harmonic balancer and a bolt on pully. The original engine is long gone. My question is what was the bolt on pully used for? It's part number is C8DE-6A312-A. I susspect it was used on 6 cyl engines which came with AC, power steering and Thermactor. I saw in the shop manual on page 8-34 spacers are moved from the front to the back of the air pump when an Air Conditioning or dual belt altenator are used. Is this correct? What else would it be used for? Please keep in mind the pully stands taller thean the 65-67 add on pully which you can buy new now. Any information would be welcomed.