You don't need a "conversion kit", as most of those kits are to convert frames with vertical drops to go SS. All you need is a quality cog with a wide base (Surly, Homebrewed Components, etc. Do NOT get stamped cogs--they will jack up your hub body). Then just buy spacers. Or, if you're cheap like me, make them out of PVC pipe. I believe it is 1.25" PVC pipe and cut them to whatever length you need. Make sure to use a table saw to get the cuts STRAIGHT. Been using mine for 4 years with zero issues.
Also, none of my wheels are SS-specific. All geared wheels with spacers.