Folks,
Changed the freewheel to the new ACS, Southpaw, 1/2" x 1/8" x 16T freewheel, and still using my lead batteries, no pedaling, got 22mph with the wind on my back and 20 mph against the wind (wind est. 10 mph). Before the change, it was 18 with the wind and 17 against the wind.
This mod is great for flat Florida. In hilly country, I don't know.

It is a "must" mod.

The most difficult part of the project, was taking off the original freewheel. I used the Parker Tool spanner SPA-1 as shown by DrkAngel, but my particular freewheel had the center part (the one that actually screws to the hub) formed over the freewheel cone, so I had to chisel it out towards the center until I was able to get the cone out as well as the guts of the freewheel and the teeth ring. After that, it was just a matter of clamping what was left of the freewheel (the center part) on a vise and unscrewing it (clockwise) off the hub.