Most 2-speed rears are set up for low and lower ratios. Sometimes you can get lucky and find a rear with the high side higher than your current single speed ratio. I had a 7.17 in my fire truck and found a 6.14/8.36 2-speed that fit in my housing making it an easy swap. It works out great as I still have low gears when I need them.
Find your local big truck junk yard and start asking questions...you might get lucky.
Mike B
