I have coilsovers for an 03 g35 coupe and I was wondering if the would work on a 08 g37 coupe. I know the spring ratio is different but would it still be possible to use?

I've always heard that it is NOT interchangeable but I've never compared the two to see why.

the difference I heard was that the spring ratio was different

I highly doubt it's because of spring rate, every coilover has different spring rates and they vary WILDLY from very soft to very VERY VERY stiff.

It's more likely that the overall length is quite a bit different but on coilovers you might be able to compensate for that by just raising/lowering to make up the difference if it's not that much. But if it was that easy then it would probably be more widely known that this was the issue.

I suspect there's some kind of mounting difference, like the bolts on the strut aren't the same bolt pattern or something along those lines.