Ok word is it a Flip Flop hub. Cause on Flip ACS is king. Other Non you need a 1.5 Diameter freewheel. I think you should bring the wheel wherever you are getting the freewheel and try to see if it works. Spacing may be issue....Can fix with washers taking off and on the axle. Or slight frame manuevering. Dont redish the hub thats sucks!

Email me if you need any more help
Sfbosoxs@hotmail.com

I had the same problem and will help at any SS gradly!