I have in mind using them on a Sky Pup Ultralight, originally
designed to use bicycle wheels w/o brakes. There is no question
that they'd be adequate, what I don't know is if they would be
heavier or harder to install than bicycle disc brakes.

Two things about these wheels:

* They have terrible UV resistance.

* They are MUCH smaller in diameter than the bicycle wheels the
airplane is designed around. This will substanially reduce your
ground clearance, and put the wing incidence much lower as well,
meaning you'll need more elevator to get off the ground.

I think Steve Kiblinger has done some work on mounting brakes on
"bicycle" wheels on his Legal Eagle ultralight. There, I've just
given you enough to do your own Google search. ;-)

Azusa drum brakes generally need a fair amount of tune-up before they
work worth a damn. The shoes generally don't fit the drums very well.
Gluing sandpaper inside the drums and dragging the brakes for a while
generally set things to right after you tear out the sandpaper, and
blow out the brake lining dust.

Me, I'd stick with the bike wheels.