Before putting anything on the tractor I tried putting the distributor cap and rotor on and turning the rotor. The rotor is interfering at one of the spark plugs. Not a lot, I can still turn it, but it is rubbing. I tried the old distributor cap and it rubbed on that too, just at a different cylinder. The old distributor cap shows visible signs of rubs for all 4 spark plug wires. So I sanded that down a bit so there was no hitting.
I'm only feeling longitudinal play, i.e. no bearing shaft play side to side, just the shaft sliding in and out a bit, so I don't think there's an issue there.
I did check and confirm that the ignition timing seems to be correct. When the rotor is pointing to a cylinder the valves are closed and the piston is at TDC, or close to it (removed a spark plug and checked for piston location). So I don't think I have a problem as far as ignition timing goes - it's either a problem with ignition itself, or a problem with fuel.
Then I hooked it all up, cranked and... no spark. Tried using the screwdriver So either my electronic ignition unit is fried, or else it really is an ignition switch issue. I haven't tried running power for the coil directly to the battery and bypassing the switch, but I have a feeling that won't help.
This has me feeling like I'm chasing my tail on the thing.