Gerry Lee, The 1929-57 Chevrolet Master Parts and Accessories Catalog lists the Group 5.001 Plate assembly for the 1951 3600 (3/4 Ton) and 3800 (1 Ton) under different part numbers. Different for Left and Right on both sized trucks too.
Others may have more knowledge on the subject, but my best guess says swapping backing plates is not an option.
~ 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)
Not going to swap over. The 3600's had 12" diameter rear brakes, while the 3800's had 14" diameter rear brakes.
Here's a page from the '51 Vehicle Info Kit on brakes.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
The axle body itself is identical between 3600 and 3800 There maybe a minor detail where the springs sit on the axle I don’t recall if there is a wider pad welded on the 1ton axle where the spring pack sits the backing plates and drums are different sizes If you need a new axle you can take the one from the 3600 but then you need to swap backing plates and all your brake parts Or you can run the whole 3600 axle and brakes on your 1 ton However that’s confusing to the future people who will work on your truck finding smaller brakes where they didn’t expect to The 3/4 ton brake drums aren’t any easier to source so there is no advantage to doing that swap The pads are available new for both 3600 and 3800 rear -s
