While the engine is at idle RPM, spray a short, light burst of carb cleaner on the gasket seam of the intake manifold where it fastens to the head. A change of RPM that coincides with your spraying indicates a vacuum leak at that spot.
Any vacuum leakage there will alter the air/fuel ratio to the cylinder.
Due to the nature of "harmonic vibration", a poorly secured gasket location might in fact "open wider" at specific RPM points, and will even erode the gasket if not repaired.

The appearance that the crank thread repair is slightly "off center" may only be an illusion.
It WILL NOT matter if the threaded hole is merely a thread or so off center anyhow...............the mounting bolt ONLY serves to secure the clutch and pulleys to the crankshaft.......it plays no role at all in centering the pulleys to the crankshaft.
Centering of the pulleys to the crank is achieved by the bore of the pulleys fitting the outside diameter of the crankshaft PTO surface.

Nice tip once again Mownie. I tried it and it does leak there, sure enough. I went ahead and took the other head off to check the gasket and while it's all there, it's also pretty ragged (meaning that it is separating into layers). I'll get a helicoil kit for the bolt and my head gasket should be in tomorrow.
I'll let you guys know how it goes. As far as running while not under load, it low idles at 1723, high idles at 3575, starts real quick and sounds smooth going up and down with the throttle. Couldn't have done it without your help.
I was hoping as much about the bolt being off-center. I noticed it was just a bearing under there anyway and that the washer looks like it should let the bolt spin using that bearing.

Got my helicoil kit in and the other head gasket on. She runs and mows great. Only backfired a little when I was in some really deep grass (about 12 inches) and it was still wet this morning. I know, I shouldn't mow when it's too wet, and I didn't mow too much, just wanted to test her out. :)

OK, good.
12" of wet grass will impose quite a load...............so if you are only getting sporadic cough back through the carb I would attribute that to some minor "hunting" of the governor.
The real evaluation of fuel ratio and cylinder balance should be done after you have mowed with it a couple of times under "normal conditions" by reading the coloration of the spark plugs.

Just an update. The mower runs and cuts great. I have an occasional backfire under really heavy load, but other than that she is good to go. I mowed 4 1/2 acres with it yesterday and some of it had gotten pretty thick while the mower has been down.
My backfiring, was either the bad head gasket on one side, or the stripped intake manifold bolt on that same side. In any case I replaced them both and no more problems.
Thanks a bunch.