Ok there are some differences. The C8 cover I have is correct for 428cj/scj. It has an extended tube cast in on the right side. Second hole up from the bottom for the cj/scj type timing pointer. It also has the pointer holes reinforced into the casting with threaded inserts. The C3 cover on my 406 does not have the tube or threaded inserts and all bolts are flush. There are also year codes on them. It has the year ex: 68 with a circle of dots around it on the face above the casting number. So they all have the same bolt pattern and gasket but if you look at a few different ones you will see the difference. I also have a C8 with a 68 date code available. It's been media blasted and painted viper blue. I did take the time to fully polish my C3 cover for the 406. Kevin, it took the better part of a week to sand and polish spending several hours a night. To read up on the timing cover and other 428 engine parts check out
www.428cobrajet.org sorry to be so long winded about timing covers. G.