If I read the OP's first post correctly, he's got an 85 Carrera, so it should be a Motronic engine not CIS. The GSC piston domes aren't that different from the stock Mahle Pistons in my 3.6. Here's one of mine:
Obviously, the valve-piston clearance needs to be measured to be sure that everything is going to work together. But, the general piston shape should work with the Motronic if the compression ratio is okay and the valve-piston clearance is safe.