The basics of the rules are posted here:

http://moutons.org/sccasolo

I think the only other possibility might be Street Mod 2, which has the rules here:

http://moutons.org/sccasolo/Rules/street_modified.html

The only thing that gets you in trouble is the engine swap. But if you read 18.1.D you see what and how you can swap engines between Mazda and Ford. It appears that a Probe could use andy Mazda or Ford engine, so a Rotary powered Probe, or a 5.0 powered MX6 would be ok, but the RX7 was totally developed by Mazda, and I can't see you getting away with that .... at least at the national level.

Now you also have to remember two things. Local people are more flexible with rules than at the national level, and it is up to the entrant to class him/herself.

This means that you can class the car yourself and it is up to someone else to protest you. I don't think your setup is completely outside of what is intended with SM. Phooka is building a 5.0 1st gen RX7, and I think his car is still within what I think SM2 should be. Granted that is my opinion, and I know the rules failrly well, but, I am not an authority.

If I were you, I would talk to the other SM2 entrants, tell them everything done to your can, and tell them that you wanted to run in SM2 and ask them if they would rather have another friendly competitor, or rather you ran in EM. I think most of them would rather have the friendly competitor and you will never hear anything else about it.

Your Mileage May Vary.