pull the battery cable
pull the # 1 spark plug
spin the motor by hand till your air squirts out of the # 1 spark plug hole. You are now in the compression stroke. Place the spark plug wires back on the engine in the correct firing order... 1-5-3-6-2-4. Make sure you have the wires in the correct order... which should be clockwise.

There is a timing mark on the flywheel. It is a steel ball that is pressed into the flywheel, and is visible with the pointer and window above the starter. The ball will line up with the pointer on the compression stroke for either cylinder 1 or cylinder 6, so it is important to check with the spark plug trick mentioned above.

if the engine is still backfiring, advance the timing a little bit.