UrS4 and 100C4 strut assemblies- what is the difference?

[TM]

Listers,
Subject line says it all- what is the difference
between the UrS4, UrS6 and 100C4 front strut assemblies?

I am contemplating doing the full UFO to UrS4 strut
conversion if it isn't extraordinarily expensive. If
the 100C4 strut assemblies are the same (possibly with
the exception of swaybar mounts- just a bracket, right?)
then the availability increases dramatically.

Does anyone know if the strut assemblies are the same
in these three cars, or is one of them stronger than the
others, etc.?

Anyone know of any for sale also?

Thanks,
Taka Mizutani
'91 200q