You probably should bring the rear springs back to original configuration.
Yes rear of truck is "modified". Who knows why. Diff does seem to be a drop out style, so may be original. PO decided to run tube down left side during some kind of swap.
Brake lines 55-59: A tee at rear of master cylinder, one tube to front left wheel, one tube toward rear to next cross member. Across front of that member to another tee. One tube to front right wheel, one tube down right frame to rear frame mounted transition bracket. Transition to rubber hose. Rubber hose to a tee mounted on axle tube bracket. One tube to right rear wheel, one tube up and over diff cover to left rear wheel. That will be Kosher and correct.
