When I dyno an engine I start with a conservative timing setting and run the first pull to gauge air/fuel ratio. For peak power look for A/F numbers in the 12.5:1 to 13:1 range. Since you will be at wide open throttle during the dyno pull, changing the main jets up or down will affect those A/F numbers. If you start out really fat, like numbers around 11.5:1, I would go down 3-4 jet sizes to get into the right range. Otherwise, maybe 2 jet sizes per change, and maybe just primary or secondary, not both. Change jets, and retest. If you start out lean, go up in size. Do you have a jet box, or are jets something that the dyno shop provides? You can't tune if you don't have a selection of jet sizes.
After you get the A/F numbers in the ballpark, start bumping the timing to see if you get an improvement. With those heads you shouldn't need a lot of timing, so if for example you were starting with 28 degrees total, I'd bump in 2 degree increments and then retest. Once you find that further increases do not improve the power, go back to the point where it stopped improving and leave the timing there. By the way, running race gas at the dyno is always recommended, because if you go a little too far in timing advance, you won't hurt the engine when running race gas.
From there, I'd be looking at carb spacer changes or any other changes you want to make. Sometimes a carb spacer will make no difference, and sometimes it will make a huge difference; I've seen a 25 HP improvement with a carb spacer. No way to predict what the engine wants, you have to test.
Dyno day can be a lot of fun; good luck and be sure to let us know how your results pan out - Jay