'65 A/C Retrofit?

I also seem too recall the A/C belt used 2 idlers. One was a fixed one beneath the compressor, and an adjustable one mounted above the alternator.

Dave is correct. The AC belt is the longest at maybe 60 inches.

There are two brackets, a large one that cradles the PS pump and an L-shaped one that the AC sits on. To attach them, screw two threaded-on-both-sides bolts (get at hardware store) into the block, then put the AC bracket on, then the PS bracket over that, then tighten all down with the nuts.
The PS bracket has a notch in it that a bolt on the back of the pump fits into.

Found this photo on an Ebay ad.