picked up a 340 long block w/out specs

Depending on when it was built, (thinking back to the pro fairground fad of the eighties) there is a good possibility that there is an antiquated cam grind and low compression piston that gives a guaranteed 6:1 dynamic compression ratio if you try to run it in a naturally aspirated configuration. If it has a distributor, it would be worth seeing if it is locked rotor or mechanical advance and what the advance rate is set for. Whole different set of tuning challenges when running an iron lung.