Although perhaps not exactly answering your question, I've used Hyperglide cogs on my Dura-ace Uniglide casette to address that same problem. Sheldon has good info on his website explaining the differences and how to modify newer cogs to fit the older freehub.
http://sheldonbrown.com/
It's a simple matter of dremeling away a bit of steel on the one odd-shape wider key to make them fit. You do have to re-use the outer locking cog, though.
Fred
**********************************
Fred Yavorsky
Jenkintown, PA
fred@twistcomm.com
http://twistcomm.com/
> From: Jerome & Elizabeth Moos <jerrymoos@sbcglobal.net>
> Date: Fri, 15 Oct 2004 10:49:19 -0700 (PDT)
> To: classicrendezvous@bikelist.org
> Subject: [CR]Shimano Pre-HyperGlide Cassettes
>
> I've encounterd some complications with the Off Topic rear hub on my On Topic
> (per KOF rule) 1988 Mercian King of Mercia. It came with 1988 Dura Ace Group,
> including a 7-speed cassette which is about a 12-19, way too high geared for
> me. I bought a 13-28 Hyperglide Cassette, assuming these were in use by 1988,
> but when I went to install it, I found the cassette is pre-HG. It has no lock
> ring, but rather the outer cog screws on to secure the inner ones. The inner
> cogs can be rotated to any position, unlike the HG cogs, which have one wider
> key, so the cog can be positioned in only one way. The outer cog has a
> different thread diameter than the On Topic AX/EX cassettes, but the inner
> cogs seem to be interchangeable, although 7-speed of course uses different
> spacers than 6 speed.
>
> How many different pre-HG cassettes did Shimano make? Do any besides AX and
> EX fall in the CR era? Did inner cogs on everything before HG interchange,
> that is can cogs from later Off Topic ones be used as a source to change AX
> and EX gearing? Does anyone know a source for pre-HG cassettes or individual
> cogs?
>
> Regards,
>
> Jerry Moos
> Houston, TX