Step 1 - Download and read the rules. Google "SCCA GCR"

Step 2 - Start hanging out with other IT drivers, go look at some cars, and go to some races

Step 3 - Ignore half of what you learn from Step 2; go back to Step 1

Step 4 - Realize that you're doing it bass-ackwards and buy a car that's already built - statistics say that you won't do this but it's worth a try to suggest it...

The short answer to your questions are "ITB" and "sort of." You can use any engine, retaining the entire long block as an assembly, from any of the Mustangs listed on the "spec line" for the car in the Improved Touring Competition Specifications.

You're actually looking at one of the cars in the book for which there are the most options available, under what we call the "update-backdate rule." I personally think that the entire lifespan of 4-cylinder Mustangs should be broken into a couple of separate spec lines but it's not current like that.

It's actually a good choice for the class, I think, and there's at least one guy who posts here who really knows about them. Maybe he'll sell you one.

Good luck!

K