Nick - I did some checking and the earliest original Chevy Master Parts Book I have that shows the parts diagrams for the spare tire carriers is a 1929-42 book. Pics are attached below. Neither show a piece that looks like the "strap" you have here. Doesn't mean it's not a part of one of the carriers, just doesn't match anything I can find. The list info does indicate there are different part numbered "straps" for other models including COE and Panel, Exp. No idea what those look like though.
The red piece is definitely a track, parts group 7.779. The '42 book lists 4 different tracks. The first is a 1/2 ton, which your track pictured seems to matches the diagram below. The other tracks are listed for a 3/4 ton pickup, a 1940 (Panel) and a 1 ton Platform. Those tracks have a different design as shown in the lower right of the below diagram page.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
