First instinct for me would be freehub swap. This will make replacing parts down the road so much easier. I think the main reason for the design above is to use a smaller tooth cog on the small end, but the problem is that if you want to ever use standard shimano or SRAM parts (which that definately is not) you will have a hard time.

Are there certain flanges on the hub that look smaller or larger? Specifically, is there a fat one followed by a thinner one? If so, then a standard Shimano or SRAM cassette should work