SunTour made different freewheels in similar and different cog to cog spacing. From symmetrical cog to cog spacing to spacing that varied across the freewheel's width. Since Ultra 6 started when indexing wasn't a thing it really just refers to a 6 cog freewheel that's nearly as wide as a 5 speed one. It doesn't really signify the cog to cog spaces, just infers they are less then the typical 5 cog freewheel's. IIRC the "ultra" spacing (what ever that actually is between any two cogs) was offered in Pro Comp and Winner grades. The difference being is how the cogs were mated onto the core and how the core was assembled. Pro Comps were usually non adjustable in the bearing preload (excepting those tiny/thin shims) and Winners used a true lock nut and cone bearing adjustment (and I have that tool set, unused for many many years). But Winners were also initially meant to be extremely flexible in what cog to cog spaces could be had, how many cogs could be mounted. In addition IIRC Winners came in a few different core designs, cog counts up to 7 or 8 were possible with later cores.

So saying Ultra 6 is like saying your car has a 6 speed gear box. Nothing about a clutch, syncromesh, ratio spread, mechanical or computer controlled.

The most straight forward way to compare freewheels is to hold then against each other or laying flat on a bench top. Then look at whether the total widths match up and/or whether the cogs are lined up between the two units. As SunTour was so willing to make so many versions that used the marketing term "Ultra 6" just reading an ad might not be enough o really tell which arrangement you get. But with friction shifting and a hub with cup and cone bearings a lot of slight mods are easy to make to have a range of reality fit and work. Andy