Oh, and a black mamba should run more spring pressure, especially with the 1.3 rockers. The 26# will bind I do believe so you have to go to dual springs. Stock size valves and only a 22mm carb will limit you but the engine should certainly be capable of 8000rpm.
What is your current ET and trap speed and the rpm your going through the lights at?
ET is determined by chassis/gearing, mph is determined by HP.
So,
you run a 9.00 at 55mph, you have an awesome setup and all the power is going to the ground. (but your low on power)
You run 12.50 at 78mph you have a lot of power but it's not getting to the ground. Maybe too much rear gear, clutch rpm too low, clutch slippage, etc.
Ideally, your et and mph should be close to what others are running. In other words, your running a 11.50 at 60mph, others running 11.50's should be around 60mph too.