Shelby U.S.A rims help??

I have a set of these rims, I bought a 1973 vw type 3 fastback off of ebay, when I arrived the guy told me that some ebay users wanted to buy the rims, but he told them the car was already sold. One of the ebayers told him that if the rims had shelby cast into the back that they were worth about $1000.00 bucks, I only paid 1800.00 for the little car , so needless to say the guy who sold the car to me was a little sick, but he said they came with the car, However , I cant find out hardly any info about these or let alone many shelby rims, someone has a post about some kind of Shelby Cal 500 rims, but these are 4-lug 15 x 5.5 , in the pictures you can make out some of the cast, the rims clean up well, I put more elbow grease in the Shelby USA cast, but the others clean up just as well. One cast says O/S 1 1/16 POS. the other is 15 x 5.5 . can anyone help me identify these rims. I am attatching pics, thanks

 

The centercaps had old porsche emblems on them.