If you just want to gain 50 - 80 horse, it's cheap and easy. Simply going to a 4bbl (my recommendation is Weiand Action plus with about a 600 cfm carb), add a cam roughly around a stock 340 (mopar performance sells the retro 340 cam), and dual exhaust (headers a bonus). For heads, I'd just have a valve job done on what you have, and open the bowl area (mildly) under the valve with a dremel. These mods listed would give ya the high side of what your looking for.