Dan, I have rebuilt a couple 313 Bascule bridges and they are not that complicated. I used the Luppold printing and inspection of one bridge assembly for working on the other. The gearbox has no springs inside and simple to disassemble for cleaning and relubrication. One bridge I have (that had been completely repainted silver!) was a prewar grey version. The gearbox on the prewar is different from the postwar, and is a more "direct drive". I enjoy my two bridges, both work fine and have been able to maintain one in original condition.
Jesse TCA