2 things you can do.
1. convert to a disc brake rear Axel
2. change the rear gears to a posi.
Open spools are famous for locking up the right rear under panic stops. If you already have a posi in it, the drums are probably your problem.
I don't see how you got both drums turned twice and still be within spec's for drum face thickness. The spec's for the thickness is stamped on the outer edge of the drum and anything thinner is shot! You could do better buying new drums as mentioned.