Now that's a serious carbine collection.
I got a "real" Standard Products. I posted about it before. It's got parts from probably a half dozen parts suppliers, as was also pretty "standard" during the war and in making repairs over the years...but mine does date from WWII. From the deep rack number on the butt it seems to have come back to the US from Israel.....who would have thought Israel... America's most favored holy place and political sacred cow.... would be selling us arms instead of us gifting them arms? Well... politics aside and be that as it may.
I also have a Universal M1 carbine. It has Hialeah Florida engraved behind the site. It was totally made for the civilian market. However, many of the parts are from leftover surplus parts. The parts must have been new surplus, although few have any marks that would suggest the source.
I took a few photos of them side by side. Without trying it out... I'd bet all parts of both rifles would exchange with no difficulty.
The Universal carbine is the one with the lighter stock. And... Universal carbines are a collector item themselves. There is link to the main Internet site in our links forum.
http://www.m1carbinesinc.com/carbine_universal.html