Almost forgot I was going to post this, I was at Gander Mountain in Grandville, MI last Friday and they had a nice probably all original SP1 on the rack.
Looked all correct, but I am not an expert on the older stuff. It looked to be in really good shape and not shot alot. Marked SP1 Colt's Lower. Had some kind of black paint spot near the pinhole for the bolt release, other than that is had a nice finish.
Bargain price of $1250. Not sure if this is good or not. If you are interested Gander will transfer to a store near you for free. Hopefully it is still there.