Just got the wheelset. The hub is a HB-6207 and the freewheel is a MF-6208. This info from velobase.com confirms that the MF-6208 fits on freewheel hubs:

"The Shimano MF-6208 Freewheel was introduced in 1986 as part of the arrival of "Shimano Index Shifting" (SIS) to the 600EX 6206-6207 Series. It consists of individual cogs with spacers which fit onto a splined freewheel body and are held in place by the threaded outer cog. Cogs are marked with the cog size and word "Index" (e.g. 24 Index) on their outer surfaces.

The MF-6208 was one of the parts in the "SIS Retrofit Kit" of the time which also included a 600EX SIS Rear Derailleur (RD-6208), 600EX Narrow Chain and 600EX Clamp-on Shift Lever set (SL-6208) with adapter parts to fit braze-on bosses. This retrofit kit allowed 6207 Series equiped bikes and other bikes to be upgraded to SIS index shifting with one installation.

Source: Shimano World, Jan/Feb 1986, Vol. 12, No. 1"