Seeing that you are going to be using the 750dp and the air gap now you need to make sure the motor is going to use all of the air fuel mixture. Keep in mind here I'm not a professional at this nor do I drag race. :yawinkle:
I would have to say that the compression would at least be 10:1 or higher. You might want to stroke the motor to give you what you want to achieve. I would stay or go with the 1.88 intake valve heads, gasket match, port and polish to get the heads flowing good and also keep the velocity up.
Read this and use your motor kind of like the 318 Bobby has built. He can help you out with any questions you might have. I talked to Bobby over the phone and I swear to you he sounds just like John Force. LOL! Trust me on this...he will have you flying with the 340!
http://www.forabodiesonly.com/mopar/showthread.php?t=28974