""2500 rpm stall TC/3:23 Sure Grip rear/255-60-15 tires in the rear.""

My stock stroke 340 in the last 13 years:
I have swapped out four carbs, two intakes, three cams, HP manifolds to TTi headers, three ignition systems, three torque converters, two different rear tire/rim sets.
For a street car, I have found the combination of the 340/2500/3:23/255 rear tires as your biggest mis-match. The 255's are a big tire to turn but I would keep them because as soon as you change your gear/converter, you will need them!
I believe that if you put your money into a good converter, your 3:23's "might" be ok. But I think that it is the combo of the 2500/3:23's that is keeping your off the line fun down.

Note: I run 3800/3:91/255 rear tires and I get instant tire spin off idle (no holding the brake) and also off of a rolling start. It is a fun street combo.