Not sure of your budget or time constraints, or the overall condition of your 340. If the engine is relatively fresh, then I would do the old tried and true bolt ons for the first money spent. Headers and exhaust, intake and carb, maybe a little better cam, and ignition. Not neccesarily in that order, but those are the basics. You can go crazy with higher compression pistons, aftermarket aluminum heads, forged internals, roller cam stuff, stroker stuff and on and on.......