Basically, the long rams weren't ready for production until 1960. Before that, inline dual quads were the "in" induction setup. So, for '60 and '61 Chrysler used the long rams. In '62, Chrysler used the short wheelbase 122" (vs. 126") and there was no room in the engine compartment to accommodate the power brakes and long rams. By '63 production, they solved the problem with a booster system in the front fender well and used it for '63 and '64, until they changed the body style again and discontinued the rams.
Russ Vaughan