IF the oil level was high, what other possible explanation other than gas leaking into the crankcase would you have?

The only one I can think of is you are initially overfilling the oil when you change it.
"Underfill" it slightly next time and let it sit several hours to run down. Then check it.

Ya, thatâÂÂs what I thought but I always check the level after I change and it checks on the line. 2 qts per owners manual. Sometimes it smokes really bad but I never have to add.

Do you have an inline fuel cutoff valve?
If not.........you need to add one and cut it off except for while you are running the engine.
Head gaskets have never been known to heal themselves and typically worsen with time.
If you saw the same symptoms last season I doubt it is a head gasket problem.
The 2 facts that might indicate you have fuel leakage into the crankcase are: High initial oil level and the smoking for 10 minutes after starting then clearing up.
As the engine heats up.......the fuel in the oil begins to boil off. This causes a higher (than normal) volume flow of crankcase gases out through the crankcase vent tube (into the intake stream). The out flowing gases are carrying very fine droplets of lube oil and some of the droplets will bypass the overwhelmed oil separator in the vent system.
For as long as it takes to boil off all the fuel in the crankcase lube oil.........you will see smoke in the exhaust.
As soon as the fuel is boiled off, the conditions inside the crankcase return to normal and very little (if any) lube oil leaves the crankcase via the vent system.
Gravity fed fuel systems are the worst offenders by having the fuel tank higher than the carb.
Even if your tractor has a fuel pump, if a portion of the fuel tank is higher than the carb, it can still leak fuel into the crankcase (if tank is full).
Carb float needle valves were never intended to guarantee to stop 100% fuel flow activity from occurring when the vehicle is stored. Carb float needle valves are only intended to maintain a fairly constant/consistent level of fuel in the bowl to satisfy the demands of the engine under all load conditions.
Install the inline fuel cutoff valve between the fuel pump (if it has a pump) and the fuel tank.

There is a solenoid needle valve at the bottom of the fuel bowl. I assume this to be a fuel shut off when the key is off. When I had the carb apart I tested it by grounding the case and applied 12 volts to the connector. It seemed to pull the plunger in.
I am going to take your advise and install a small ball valve in the fuel line before the pump. Although I'll have to leave a note on the steering wheel to open the valve before I start the mower next time.

"There is a solenoid needle valve at the bottom of the fuel bowl. I assume this to be a fuel shut off when the key is off."
A lot of folks presume the solenoid valve will stop ALL fuel flow (when key is off). That is not what the solenoid valve is for. The solenoid valve is actually to prevent/minimize the occurrence of "afterfire bang" out the exhaust when you shut down the hot engine.
The solenoid valve only stops the fuel in the main jet. There is still a pilot jet (idle fuel), and an internal overflow vent (usually) that can still pass fuel to the intake and on to the crankcase if the float needle valve fails to completely block fuel flow.
Essentially the collective industry (engine & equipment OEMs) are dodging responsibility of the problem and have opted to eliminate a manual inline fuel cutoff valve to save a few bucks on their bottom line.
They uphold the excuse that the float needle is supposed to be adequate for the task. In a perfect world that could be good enough. However, in an imperfect world, it is best to take care of their inadequacies by installing and using a manual valve to protect your investments.

"Although I'll have to leave a note on the steering wheel to open the valve before I start the mower next time."
Better you leave a note to remind yourself to turn OFF the fuel valve when you stop the engine. If you fail to turn the valve ON.........the engine will let you know pretty quick.

Added the fuel shut off. Drained and replaced oil to fill mark on stick. Started engine and it smoked pretty bad. I let it run about 5 min. varying the speed up and down, smoke diminished a little but still noticeable. Shut engine down. Checked oil and it had a light foam on the stick. It was not overfilled. Started engine to put tractor in garage and no smoke at all. I ran it around the yard, no smoke, put it away and will check tomorrow.