After doing some research of those wheels that SIG used in their prototypes, I think those were the OLD DuBro wheels (when they had chrome hubs). I've only seen one pair on Ebay a while back....and they were in an assortment of other stuff I didn't need.
The Kavan wheels available from SIG, look very similar, and are much lighter.
I was able to source an original type Semco Super Muffler, Part #203FS. That took some time to find. lol