Have you tried Bob's Gear Ratio Calculator? It uses fairly close estimates of the torque and power curves, and you can put in whatever gear ratios you want to see how they'll work.
But once you know the torque curve of the engine you'll never need anything to do with a dyno. Just overlay torque curves multiplied by the gear ratio (basically), and you can see everything. Then you need to overlay a drag curve, to find what you're top speed is.
But, the best way is still to get out there. Set the gearing for the end of the longest straight at roughly peak power, and the two lowest gears for good starts and the slowest corner. Then space the others evenly (pr perhaps tweak the evenness to suit particular corners if you think it'll gain you time).
There's just no need for a dyno no matter how thick you are.