I agree with the short duration cam choice. With 3.23 gears and low compression, no more duration than a stock 340 cam will work well. If there is a cam with similar duration but more lift, I would look into that. If you can back cut the stock valves, that will help. Many years ago I did that with a drill press to spin the valve, and an angle grinder. Ugly, but it worked. A 340 with low compression and a 268H Comp cam ran very well done that way. Be sure and run the thinnest head gaskets you can get, and block off the heat riser crossover if you can live with a bit of a cold blooded motor.