I agree with kursplat. You have a great starting point here. No need to go crazy just yet. Get all your tuneup basics covered and then use your test equipment to help determine the health of this 340. Cylinder pressure, vacuum reading and timing. I would also like to see a oil pressure reading with a mechanical gauge. These numbers will give you a very good idea of how this engine is doing...hell, maybe get it on a chassis dyno. That being said, I would get the headers going.