I bought a 2-sheave pulley from an outfit in California several years ago. The damping rubber let go after a while and the sheave stopped turning. I'd seen them slip on the Ford pulleys which produced overheating problems that took a long time to figure out. Anyhow the Damper Doctor people replaced it at no charge in just a couple of days. No trouble since. Been ten years.
You really do need 2 sheaves. I had the single sheave setup I bought from Patrick's while he was living. It ran the alternator off the extra sheave on the compressor. It worked fine in the short term but the combination of loads from fan & WP, alternator and Sandon compressor wore out the belt too quickly. I'm still using the Patrick's brackets but there are a several problems with that. 1) the alternator is mounted too close to the exhaust manifold. Melts the grease out of the rear alt. bearing. So I had to make a heat shield.
2) The combination of belts requires that the AC compressor be swung so far out that it starts coming back in again if you rotate it any further. So I had to build a 1/2 inch shim to go under the compressor. It mounts on the old generator location.
3) The shimmed compressor location puts it and the lo side hose fittings too close to the exhaust manifold necessitating another heat shield.
4) The Patrick's alternator bracket only allows one of the alternator pulley sheaves to be used - The front one. Since I haul a camper with two golf-cart batteries for the house batteries, he alternator is called on to charge the house batteries if they are low and it really should be driven by two belts. Without the load of the house batteries things would probably be OK as is - Except, except that when the AC/heat system is in defrost/de-humidify mode it runs the compressor and the blower fan and it's usually raining so the lights are on, including the running lights for the camper, oh and the wipers, which now are electric, and after a while if you're in traffic, whenever you pull off from a traffic light the belts set up a howl like a hound with a coon up a tree. It eventually stops but it's annoying.
Since you won't be buying Patrick's brackets you won't have my specific problems but other bracket kits may cause similar problems. So mine is a list of things to watch out for. There are many pitfalls. I ran into a similar set of problems shoehorning a 350 Cummins into a 59 KW long nose and then mounting AC on it. The compressor mounting was just the beginning.
Whatever AC kit you buy, if it comes with the service-port fittings mounted on the compressor fittings, throw those in your junk box and buy some without service fittings. Buy fittings to put the service fittings on the receiver/dryer and on the low-side fitting where it comes out of the firewall. I had to do this after it was all built and I had burnt my wrist a couple of times. Also the service port on the compressor fitting is too close to the fender well to connect the gauge set without moving the compressor connecting and then moving it back. Repeat to disconnect. Not only that but the service port hits the exhaust manifold before you can get enough slack in the belt to change it. This requires removing the fan and WP pulley to slip the belts on and off. This isn't the end of the world but adds a half hour to the job.
Try to avoid buying an evaporator kit that combines the evaporator and heater core in one unit. These don't drain the water off the evaporator well AND you can't get a high enough temperature out of the ducts to be comfortable without the windows fogging up almost instantly. The unit I bought was from HotRod Air or maybe it was Old Air in Texas and they are now out of business. I think the ones you see from Vintage Air use the same combined evaporator/heater combination. I think they do that to save space. You might call and ask them.
If I had it to do over again I would try to adapt a factory air system from one of the Big Three, hopefully one that uses an expansion valve rather than a capillary tube. I'm not sure about the disadvantages of cap tubes but it's always seemed like a cheap way out to me. The more expensive cars all used expansion valves in my experience.
