mystery brake drum part #

[dlb]

hi guys. new to this forum and chevy's in general. i have some old GM brake drums that i need to replace and am wondering if any experts here might be able to point me in the right direction.

here's the story. my wife bought a home-built horse trailer that i've been fixing up for her. it's been a headache because the spindles and brake stuff are apparently from WWII military surplus, or that's the best guess of the local antique/classic/vintage gurus. i got the brake shoes and cylinders refurbished with no problem but when i took the drums in to be turned, we found that two of them are bent all to hell. there is a raised part # inside the drums which is

GM 6387631

i've searched that part # all over the place but have found no matches. i'm told it might just be a casting #. the drums measure 11" X 2" and are riveted to the hub, which houses the bearings. i'll try to post a few pics to give a better idea.

if anyone can tell me what these are originally off of, where i can find new ones, or any other pertinent info, i'd really appreciate it. i know i could just toss all these old parts and buy new complete replacement stuff but we've already sunk some $$$ into this so far and would prefer to not have to take a few steps backward before moving forward again.

thanks!