I get about 7100 rpm with a 16x8 prop.

If you converted it to EI that is what you should get too. If you did not convert it to EI I'm not sure what you should expect. I know that you want to advance the timing for more power though. There are a couple of ways to adjust the timing with the mag:

1 Move the pick-up coil about 1/2" clockwise standing in front of the engine.
2 Take the flywheel off, you'll see a slot for a woodruff key. With a dremel tool make another slot about 1/8"to the right of the slot that's there.