Trying to sqeeze more out of my 340

Your cam specs are a good match for the heads. Your rpm range is way past what they will flow efficiently. These heads will run out of air past 6300 6500 rpm. Above that your HP & TQ. will fall off. What header size do you have (1.75 in. here) and how tall a tire are you running? The 904 maybe a little quicker because of the size of the components but it is also has half the strength (life span). Did you install forged hubs in your racing TF? I'd go to a 4:56
I ran 11.3 comp, ported J-heads (243 cfm), mopar solid cam .528 lift, M-1 manifold, 750 dp, 3800 stall, 727, 4:56.. 11.33, 118+