Pulling the head on that little two cylinder engine is real simple, no more complicated than a starter or water pump except several times longer to do.
The only parts that are critical are cleanliness, head bolt torque, and adjusting the valves and the compression release. And don't drop the pushrods down into the pan.
All the rest of it is 'well this is in the way so I obviously need to take it off' like the air cleaner, fuel lines, etc.
You must already have the fan shroud off and that is maybe 10% of the project right there.
If you have to work outdoors, you might work over a tarp to catch anything that falls. You can still drive the tractor a few feet without coolant in it, if you need to move to a carport or something.
Given the location of that broken bolt I think it would be impossible (for a weekend mechanic) to accurately center punch a starting point for your drill and then drill in perfectly straight. - into that tempered ezout that probably didn't snap off perfectly flat.