When I worked for GM as mechanic I use to install after market a/c on cars when new . The kits all came with that style compressor and were all mounted up on top of the engine in the middle with an extra pulley installed . The compressor was bolted on from the bottom with 4 bolts . The compressor should be using a belt by it's self with the V belt . Just my opinion . Retro Jim
Those brackets are easy to find in wrecking yards or probably new for a very low price. What you have is going to be in the way of everything before you get done. Go to the wrecking yard Start looking under hoods of 70's and early Chevs that may have a V8 in them and see if you can find the correct bracket or someone on here may have one laying around in a box that they would offer up for cheaps. The Jeep guys have a good article on hooking one up to use for air here http://www.offroaders.com/info/tech-corner/project-cj7/project-cj7-onboard-air.htm
There's also a ton of info here: http://www.kilbyforums.com/ I've been running a york on my jeep for years -love it.
PUT THE ENGINE IN THE CAR! You can spend weeks jerking around with this and that sitting on your garage floor but until the motor is mounted in the car you won't really see where the clearance problems are. Trust me - all the measuring and figuring in the world won't make up for 5 minutes of looking at the motor, frame, radiator support, and inner fenders all sitting in their respective positions. And as for the alternator being close to the exhaust manifold, up until the late 1960s long water pump they bolted directly to a bracket ON the exhaust manifold. I'm sure that's not ideal, but you get the idea that it can work really close.