Thanks to everyone who replied.

My LBS (populated with serious and very helpful cyclists) has a tech who pointed out that I'd crush the bearings if the shell width were off as much as the caliper says. Reason enough to get the shell faced.

On the other hand, Cannondale is thought to have been better oriented to proper dimensions, and so I may just have a bad caliper.

So, step one is to make sure the dimensions are either correct (the caliper is lying, and so time to get a new digital caliper), or not.
If the shell is overwidth, get it faced!
If not, install the UT crankset and go for a ride!

Thanks again, everyone.

JF