jer wrote:I will be using it on an American Classic. The freehub bodies on those are, i believe, aluminum. I think the ultegra is steel.
Yep. The lone 28t I used in the Death Ride last year notched my aluminum American Classic freehub body. Not badly, but I didn't use the 28 much. This year I used a normal 12-27.
I thought of making a wider splined interface on the 28t by cutting the inside out of a worn cog and welding it to the 28t but didn't get around to it. I don't think that epoxying a spacer to the 28 will work, its the wrong kind of joint for glue.
Maybe you could get the last three cog spider off a MTB cassette and mill off the large cog.