Pontiac Firebird mounting kit?

I have the standard mounting kit that's easily available for 1993 and up Firebirds and Camaros and while it worked fine with other head units, the empeg doesn't line up flush with the mounting plate. Does anyone know a better kit for this?

Can you be more specific? For instance, do you have a digital camera and can show us a picture of what you mean by not lining up flush?