Was there a "Shelby" casting company supplying aluminum parts to Ford? Ran across this on eBay, I don't know what it is for. I had a aluminum rear window stop that I took out of a 1965 Mustang coupe which also had this same marking. I don't believe these were cast by or for Shelby, just curious.
David
https://www.ebay.com/itm/Lot-of-2-New-NOS-Shelby-1-2-5-8-Hose-Y-Manifold-Nipple-Aluminum-Fitting/172631356371?hash=item2831a173d3:g:QB4AAOSwvihY9iI~
(https://i.ebayimg.com/images/g/QB4AAOSwvihY9iI~/s-l1600.jpg)
(https://i.ebayimg.com/images/g/tOgAAOSwBOtY9iJM/s-l1600.jpg)
No connection to SAI. Those are die cast parts and IIRC the casting company was in a city named Shelby. I might be wrong about that part but not the no connection to SAI.
Randy
I'd bet it's from this company:
http://shelbytube.com/products