When running with the anti-oil fouling pocket heads, one does need to use more advance for the ignition. My '34 OHV seemed to be happy with 35 degrees advance. Heads that have been drilled out have faster ignition and so should be set up with less advance and I have heard numbers closer to 25 being found suitable.
I can not see that as being a problem with the 2-3/4hp engines though, as they do not run fast enough that ignition speed should be a problem. So if the plug is recessed and you have timed it a little early, no big deal. The twenty extra nano-seconds that it takes to light the mixture is not going to stop the engine from spinning up to eight thousand RPM, because the crank and rods will break long before that point is reached!
One thing I found with my old Ford is the ground electrode tended to shroud the spark, and there was not enough turbulence in the low compression and minimal squish head to get the mixture lit off to a good start at slow speeds. Cutting the ground electrode short and bending it down to the side of the center electrode made for improved low speed running. Of course, this severely limits your re-gaping options!
-Doug