Help me understand my 8-speed uniglide compatibility issue I have a Dura Ace 8-speed uniglide rear hub/freewheel marked 'Integrated 8 SIS' and an 8 speed uniglide 14-21T cassette.

Two issues - the first being that the smallest cog needs to be a special 32mm Dura Ace thread, I think this issue unrelated but include the info in case it is. (32mm 14T Dura Ace cog on its way)

The actual issue I'd like to clarify appears to be the size of either the cassette or the freewheel on the hub is incorrect. 

If I stack 8 speeds I run out of splines and the second to smallest cog (15T) would just spin if I were to apply torque:



If I try 7 speeds, I cant thread on the smallest cog as it'll hit the splines:



If I add a spacer to the 7 then it appears to all fit. But it's hardly correct, this is meant to be an 8 speed system right?? :



Measuring the pitch I see that it is indeed 8-speed (4.8mm), yet the stack height appears slightly larger at 35.85mm (it should be 35.4mm) - probably due to the smallest cog and the black spacer (0.3mm thicker than the others).



The only way I can see to maybe get it working would be to turn off some of the uniglide splines on a lathe and use two Dura Ace threaded cogs (14T and 15T) - the 15T one wouldn't have as much thread to work on in this case. Or perhaps running pins through the 3 holes that run through the cogs and spacers?? I am yet to check if doing that would leave enough room between the smallest cog with chain on and the frame..

Edit: Another option is buying another 32mm threaded Dura Ace cog in 15T and turn/file/mill out the uniglide teeth on it for use as the second smallest cog (14T would be another 32mm threaded Dura Ace cog)

Hopefully this is something basic I'm overlooking? ;)
This is not my area of expertise, but at first glance you have a 6/7 speed freehub body, not an 8 speed as you thought.

I see the threads on the 8 speed are cut into the splines, whereas yours has a continuous thread all the way around, but its lower than the highest part of the splines.

Some photos thanks to google images:





Images from https://www.bikeforums.net/classic-vintage/626072-dura-ace-freehub-id-7400-7402-7403-101-a.html and theres more info there.