67 Shelby Block Engineering Casting Numbers

FW: 67 Shelby Block Engineering Casting Numbers
Group,

I am looking at two 67 GT 500s and have a question on the blocks. The early car has a C6ME-A casting. Should or could it have a C7ME-A? The late car casting number is not really readible due to heavy rust on the block. Should a late car (Above serial 2500) have a C7 or C6 number.

Thanks,

Rick Thompson