Is it legal in SCCA IT to change a E30 318 chassis to 325 specs? If this change is made do you have to take the entire drivetrain from the 325?

I know I need a GCR, but I currently run a Trans Am under CACC rules here in Canada, which has to run ITE in North Pacific against high dollar 911/Z06,etc. I would like a more competitive/cheaper class and found a 85 318 with a dead drivetrain.

The fact that I'm a BMW tech makes the car choice simple, finding the parts is not an issue.

TIA