Are 1966 Mustang and 1967 Mustang idler pulleys interchangable?

I believe that they both go from the alternator to the waterpump. From what I have researched, the pulleys, idler bushings, and waterpumps are interchangable. They appear to be identical but I'm unsure about the bracket itself and the actual placement. I have seen a picture with one attached from the top of the alternator to the two lower left blots on the pump and the other with two bolts on the altenator and one on the waterpump.

Disregard the "two" different installations. It goes from the altenator to two bolts on the waterpump. I found these photos on-line (not sure where though unless I'd just link to it).

OK...I'm a resto-mod guy and not a pure resto so I may be wrong here...but why do you need the idler pulley anyway? If I understand it right the only reason for an idler pulley is when a belt driven accessory is mounted "upside down" and needs to be driven by the "back side" of the belt to rotate in the correct direction. I wasn't aware of any Mustang before the mid-'70s that had any kind of "serpentine" drive that required and idler. Also, in the pics it looks like a v-belt pulley. Will an idler even work with a v-belt? I thought they required a flat/grooved belt. Is this a resto or a "modified" application?

Like I said I may be WAAAYYYY wrong...I'm more curious than anything.

Looking through some diagrams, I found the idler pulley was installed between the crankshaft pulley and the A/C comp. pulley on the passenger side. It's purpose appears to be to allow for adjustment of this dedicated belt. Another belt is used for the alt. and P/S. and water pump.

The placement of the idler is in the same place on 66 and 67 cars, but the brackets are different. Unless you are using an A/C compressor, which is rigidly mounted, there should be no need for the idler.

In 67 there were two different idler brackets. One was used for factory installed A/C, the other , dealer installed A/C.