Great (on the compatability) The clusters are held togeather by a long rivit setup.Grind the rivit head off and...
This (interchangeability )will afford me the cogs I needed without needing to purchase more complete cassettes.
BTW apparently the newer cassettes DO come completely apart.
I upgraded my 08 Ultegra equipped bike (went with the 6750 derailleur so I could use a 11-28 10 cog cassette)
Had the LBS do the changeover and when I got the old cassette back it was held together with a zip tie, cogs completely free of the body. Apparently Bikes Direct had the origional 6600 cassette upgraded and that required disassembly of the origional cassette.
Anyhow, Thanks HillRider!