I should have known this. I sold three Genuine Porsche Austausch Motorola alternators for $700 outright somewhere in November, they'd been sitting on the shelves for way too long. Three for less than the price of two., 'new' in box.
I don't think that grafting a non-Porsche alternator into a Porsche fan/ring combo would really save a lot of money on a one off basis, I am affraid it would be more expensive even, unless you can do the machining yourself. Then you still have to fit an adjustable pulley, and the bearing problem comes to mind, the Porsche alternator was designed with the thrust loads of the fan in mind, the 3.2 Carrera pushing 1500 L/sec @ 6000 RPM (source: Porsche factory workshop manuals), that's really a whole lot. The Porsche units shouldn't be so hard to find, there are many engine upgrades in the Porsche world and just the pre 3.0 engines are getting really tired by now, just be persistent, the guy selling you used Porsche parts doesn't show you his stash, but really, 944 trailing arms for instance, I've seen them stacked up to the roof and they're rarely needed by 944 owners, just think of it, when was the last time you needed to replace an IRS arm on a Bug? The alloy arms do break from time to time, but the demand is really not high. A lot of the parts that we use on VWs are not in high demand, the early 944 brakes as well, I know two used Porsche parts places that won't even drive up to pick up a 924 or early 944 for free. A friendly approach to these guys can do a lot.
erh .. I hope it helps
Brian