RE: 340 or 440-6
Being I've never rode in a 340, my answer is to go with the 440 6pack. In 74 and later they raised the compression the 440motors, which doesn't to me mean to much. It still has great potential, and with the right parts can easily be made into a beast.
You will definiatly get alot more reaction with the 440-6. I get more people asking to see the motor, even though it's clearly marked asking does it actually have a 440-6 in it. Even when i had a 440 charger, this gets way more attention.