In GT1 you must have a standard production block and heads, unless the heads are on the approved list.
The induction would have to be a 4 barrel. Fuel Injection was prohibited on GT1 cars 1/1/94 IRS is ok as long as the car came factory with one. You can replace it with a live axle. But, cant add IRS to a car that came factory with a live axle.
Steering is open, so R&P is ok.
The weight factor is why so many GT1 cars are running the small 311 engine.
You can cut your weight to 2680lb. Weight penalty for more CI's up to a 366ci.
Wheel base for the c3 must be 98" C4 96" and the 97 up 104.5
I always found this interesting, SCCA GCR 9.1.2 The Club may alter or adjust the specifications and require, permit or restrict certain specific components to equate competitive potential... so if you win to much, be ready for a rule change,,,lol.. They have been doing that to Tom Patton on his Sunbean Tiger for years, he's down to running a two barrel.