OK, when you said "new plugs" I assumed you meant you had replaced them AFTER the starting problem cropped up.
Here's something to try before your parts come in: Take out your spark plugs and burn off any carbon using a torch or a burner on your gas range. If you do this using an acetylene torch, use a slightly oxidizing flame and be very careful not to melt the electrodes. I'll bet your tractor will fire up with the cleaned plugs. Try starting initially with no choke and open throttle, as there's probably already plenty of fuel in the cylinders.
When you replace your plug wires, be sure to use resistance wires to protect your Pertronix unit.