Success for me so I'll share what finally did work. Previously, what didn't work: 1) heat while under tension with a puller, 2) an impact wrench on my harbor freight puller till it stripped the puller screw, 3) an Autozone harmonic balancer puller with impact wrench till it broke one of the bolts.
I read in other posts that it's not as important to get a lot of force on the hammering on the end of the shaft as it is to get a sharp pop. I also read in some other ones that putting a LOT of tension on the puller could be distorting the tapered hole in the flywheel and causing it to clamp down even more on the shaft.
For those with stuck magneto flywheels looking for another trick or method to pop it off, here's one to try. It's a variation of the traditional procedures. Let's call it the Texas Method of flywheel removal. If yours is stubborn like mine was as well as the authors of several videos online are (see flying flywheels), this might get you on your way.
I put the harmonic balancer puller on with some replacement bolts (since I bent all the original ones) with some stacks of washers to keep the bolts from pulling down thru the puller slots. I chained the engine down so I could twist it with a breaker bar. Of course, I had already secured the crank by stuffing the near cylinder with rope and running the piston up as far as it would go, and tethered the puller with rope to support it after it pops so it doesn't drop and break any teeth. I also had the other end of the crank (PTO flywheel) lifted off the surface by putting wood blocks under the engine and mount. You want to give the crankshaft somewhere to go (slightly) when you are pounding on the other end.
I installed the puller and eyeballed the alignment of the puller bolt with the mounting bolts to make sure I was pulling straight up. I put the puller under a little bit of pressure and took the lightest hammer I have and rapped hard on the puller bolt about 10 times. Then I tightened the bolt about 1/4 turn and rapped 10 more times. I repeated this 3-4 times till the pressure started getting serious. Then I tightened about 1/8 turn and did this 3-4 more times until the flywheel finally popped off.
If I'm correct, the idea is to hit the sweet spot between pulling pressure and keeping the hole undistorted. Since you don't know where the sweet spot is, you use an iterative process by gradually adding pressure in hopes that somewhere along the spectrum you will find the right combination. I would say if you get the puller so tight that it starts bending the puller or breaking the bolts, you are too tight so start over. Keep lots of oil soaking on the shaft while it's vertical to give you every advantage you can. Sorry the pics are dark under the shadows.