1. It's slightly larger so you will need to do a little grinding and filing of one of the brackets which isn't really a big deal.
2. The pulley is a 5 groove pulley and not a 7 groove pulley.
On the advice of friends who know alot about cars I've opted not to just put the 5 groove pulley on at first. I'm going to try out swapping the pullies or ordering a new one first. If those things don't work I'll use the 5 groove belt.
I'm still waiting for the delivery of my new alternator (the other was damaged in shipping) but when I get it I'm having a friend of mine see if he can swap the pulleys or modify the old pulley or order me a new one since he works at a machine shop.
If you havn't done it by then I'll let you know how it goes.
Dont know about the mk3 alt. but a 85 cresseda alt and its mounting braket fits well and all that needs changing on alt is pully and the plug on the alt is diferent so chang for the cresseda plug. 85 cressida runs a 5m mtr just later model alt and mounting bracket prob same as mk3.
Why settle for a Mk3 alternator? I've been running a Mk4 alternator for a year and a half now (almost 2 years) and love it! 100 amps kicks ass! I've got a relatively big stereo system, twin electric fans (20 amp draw!), 100w foglights, and now even with all these on, and the rear defrost and wipers, the voltage level stays above 12V. It's great! The alt is an Auto Zone rebuilt unit, part number 13240 for a 1996 Twin Turbo Automatic. Cost before core is about $180.
The pulley is 6 rib instead of 5, which helps somewhat. I heard that going to a 6 rib belt instead of 7 would shorten the life of the belt, but it's been on there the whole time and it's doing fine. This will only work on a 6M or 84 or later model 5M.
If you have an 83 or earlier Supra, you'll need to remove the charge light relay and replace it with a diode. I have the info on this somewhere, and it's super easy...
The bracket mods required to do this are similar to the Mk3 requirements, and I even have the Toyota part number for the Mk4 alternator clip, which is about $10, wires and pins not included. It's 90980-11349. The guy where I got mine immediately knew which wires to get and they were about $6 apiece.
You'll also need to find a 3" or so bolt, a nut, and a bunch of washers to replace the upper mounting bolt.
I'm using a 38" 6 rib belt, from Auto Zone.
I have pics of the bracket mods and the upper bolt replacement. PM me with your email address and I'll send them along to you.