It is very simple with either an a/f gauge (road test) of on the dyno with an a/f reading. You want to achieve a flat 12.75 a/f curve at wot from 3000-6000. All you have to do is to first (pre dyno)plot the injector pulse widths from 3000 to 6000 rpm. At the dyno as an example, if you are 12.0 (rich)instead of 12.75 at 3500 rpm, that is 6% low. If you had a pulse width of 13 mS, you would merely pull 6%, or .78 mS at 3500 rpm.
The timing is only set after you have achieved the flat a/f curve. The timing requires more care, less advance at peak torque and more advance in the higher rpm's. The a/f changes very little with changes in timing, you have to go by hp and your ear.
good luck