Since the engine has a removeable backplate/drum rotor, you should be able to rotate the backplate 90 degrees counter clockwise (when viewing the backplate directly) this should make the timing correct for reverse rotation running.

(I may have the direction you want to rotate the backplate wrong, but it is simple to see with the engine in your hand as you want the rotor to open up as the piston starts on the upstroke)

AJC