Thanks everyone for your input. It sounds like these square bearing thingys
are a rather recent innovation (if it is in fact that).
I ended up buying a Whiteside 1/2" shank 1" CL flush trimmer with the normal
round bearing guide (works great, BTW). The local Woodcraft did not even
have a square one to look at (sorry, Slowhand). Someone else is going to
have to experiment.
And Leon, good catch on the inside curves issue. I had not even thought of