The C5AW is the engineering number on the pinion support not the main housing itself. Without seeing more pictures, the date would probably be 1969 if it is a C4AW casting. If it is a C7AW, it could be 1979.
The C4AW would have two external verical supports, The C7AW would have only one. Those casting numbers are on the inside of the casting.
There are no C7AW housings originally on any Shelby's. The are all C4AW.
I can post pictures of both in a while if you need to see them.