There are no "exhaust plates" on 67 or 68's. 69 only. What you will find are 2 holes (holes were for nut inserts for the tailpipe hanger) for the dual exhaust mounting on the frame rail. Post up photos from all angles of the engine compartment, firewall and as David suggested post up the diff stamping and casting date photos.
You can find more info on where to look etc here. ====>
1967-1969 Drivetrain - Axle LinkYou can also go here and start clicking around and reading. It will help you and possibly answer any more questions you might have before posting questions that may have already been asked. Good luck and congrats on owning the best 1st gen year (1968).
Camaro Research Group Index Main Page