I'm thinking your piece is from a Bonneville.
The top dimension that you show as about 34 1/2" is only about 31 1/2" on the piece on my CS.
Also you show 3 mounting tabs along the bottom edge and mine only has 2 mounting tabs.
Don't know if that is good news or not but it sure opens up the market for it. On the other hand, being longer, it is probably quite adaptable to use on a CS.