Bigger Carb on my 340

Dave's advice is good (eg post #20)
You will do will with money on a rods, jets and springs coupled with some tuning time on a dyno, or at the drag strip or other repeatable venue.
If you haven't looked at the spark plugs, they'll give you at least a general impression of what's going on even if you're not an expert in reading them (that's a bit of an art). Start with a new set before the first dyno or 1/4 mile run. That way you get a clean read of Wide Open Throttle. Same when you do your around town or highway tuning.