There's nothing wrong with the older Motorola alternators, other than they're all getting old, and are expensive to replace. The Delco alternator used by Chevrolet is common as dirt, half (or less) the cost, have twice the output, a built-in voltage regulator, and one minor problem: the case is a bit bigger than the smaller Motorola.
This covers getting the alternator physically installed; wiring it is easy and can be found on the net.
You can buy a new bracket from a speed shop or Summit's, or you can hack up the existing Motorola alternator mounting bracket to accomodate the wider Delco. The photos below show how I simply drilled out the spot-welds to split the two bracket halves, redrilled it for the right width, and stuck it back on. It ain't rocket science.
The problem is that the Delco is big, and there is barely enough room for it; it wants to interfere with the block in one direction, and the steering gear in the other. With manual steering, it just fits, as-is. With power steering, there's not enough room to adjust the V-belt.
Matt Hass worked out which fan belt will make it fit (see below). Or you can file off Delco housing aluminum to fit (I can't bring myself to do things like that) or find a compatible "one-wire" alt from a furrin' car, or there may be Delcos of smaller diameter.
From: Matt Haas Subject: The belt you need for a Power Master alternator on an early 6 with power steering Date: Mon, 02 Aug 2004 21:29:57 -0400 I found the size belt I needed to get be able to fully tighten the alternator belt. The belt I used is a 36" belt (Dayco 15360) which is just a half inch shorter than stock. I now have about 3/8 inch between the alternator and the steering gear which is just a little more than I had with the stock belt and Delco alternator. To summarize the entire alternator experience I had this weekend: Manual steering + Delco alternator = stock belt Power steering + Delco alternator = stock belt Manual steering + Power Master alternator = stock belt Power steering + Power Master alternator = 36 inch belt This should apply to all 1964-74 Series 01 AMC's with a six cylinder. Matt Cincinnati, OH http://www.mattsoldcars.com