Starter solenoid and ignition switch is not likely to be the issue.
You say the PTO clutch is unplugged and the PTO FUSE blows when cranking the engine.
If so
Might try these hints: (leave the PTO clutch unplugged at the connector by the PTO clutch)
Instead of guessing and throwing parts at it might try this.
Take a 12v bulb with a bulb holder (for example one of your lawn tractor headlights and it's bulb holder) and remove the fuse and connect the bulb (both wires of the bulb holder) in place of the fuse.
Normally the bulb will not light up. When you see the bulb glow that circuit has a short to ground. When first connected just turn the key on WITHOUT cranking the engine wiggle the wiring harness, etc and if the bulb flickers or lights up it's seeing the overload/short, if nothing start cranking the engine and watch the bulb.
Let us know the results
Also if that is a automotive type blade fuse you can get a circuit breaker very reasonably priced.
If you see the bulb light up constantly disconnect the battery and use a ohmmeter. Best to not use a ohmmeter with the battery POS connected or the Ohmmeter will get smoked. (ohmmeter do not like being exposed to a voltage)
