Thanks for the info.Height seems to be the problem.I have the 80 mod seats with the plastic back and base and you sit low in them.I have a set of OBX seats from a previous project and with them in the vette sitting on the floor without rails you sit a fair bit higher,doesn't feel good sitting up high in a vette.Thought the C4 might be lower being they came from a similar height car but looks like GM lowered the floor pan a bit in the C4 where the seats mount.
Will have to see what else will fit.