So I'm getting ready to rebuild a 340

Sounds like you should pick up a set of speed master heads from a member here named IQ52, have him do a lil work to them , nohing insane, then get a cam around [email protected] of duration and go with enough lobe lift that it will use the heads configured capability. Stay around 9.7 compression, and get a set of 3.55 gears , dual plane Edelbrock rpm intake and some 'what ever' headers. It will be a no headache motor, not finicky with octane ...It'll pull tree stumps , fry tires and cruise with reliablity for thousands of miles. Now...if you have a lil more dough...go hyd roller on the cam and a set of roller rockers to back it up.