They may use the same type of device that I mentioned earlier. That is really not a "substitute" for a 3-wire. It is as Dave said probably only good to let you know a belt broke or that you need to rev your engine up.
I would ask them how that works with a one wire. It doesn't provide sensing just a warning.
Dave has covered this before and has wiring diagrams or you can go here to get a good overview of 1 wire vs 3 wire.
If you decide to use the GM alternator you can get a kit from Mark Hamilton on that site for either the CS or SI. They are about 10 bucks more than listed as the site prices are not updated.
Even with the kit and buying an alternator from the parts store you will be money ahead.
One thing I like about Mark's kits is that he includes good info and fusible link wires. They do need to have the butt splices and ring terminals installed on the wires but the instructions are good.
He also has a book "Electrical Wiring - Tech is Made Simple" for $8.95 that I would recommend that is VERY Good. It helped me to understand such things as "Thermal Runaway".
Another alternative is a Ford 3G alternator to keep it all Ford and follow Dave's wiring diagram.
Here is just one source for New not rebuilt alternators:
Here is an older thread that may be helpful: