the old h70 snow king is a good motor. its a big torque monster at real low rpm's because its a big displacment engine.
the honda gx is also a good motor, got good ammount of torque, but its torque is turned for a bit higher rpm's, probably around 3000-3600 rpm's where as the tecumseh make all its power down low around 1500-2500. the honda has overhead valves so its a more modern dsign that makes more power in a smaller size. its also more efficent.
if it were me, i would replace the tecumseh with the honda. sell the tecumseh on ebay! plenty of people sill buy it from ya. i think go carters like that block.
the honda probably has electronic ignition, something the techmseh does not. the tecumseh ignition points is behind the flywheel. so if you have an ignition problem you have to remove alot of parts just to get at the points.
with a winter jet kit, the honda will probably run better, be more efficent, and quieter.