Yes, I too had heaps of these as a youngen. I built several as an introduction to two wheel mania for my little brothers etc.
You can achieve a nice close ratio outcome by mixing and matching the tranny clusters from sl/cl/cb 100's.
There is a hell of a lot you can achieve by openning/ enlarging the air/carby/inlet supply/ports/megaphone exhaust etc.
If you want step out of 125 class, just drop in a xl/ct185 crank = 153cc, for fun.
Don't get caught with a two piece head in pre-75 though.
I am pretty sure that leading axle CR125 fork sliders share the same part# as the latter CT's.
I doubt I will ever get around to it, but I always wanted to introduce a certain camshaft onto needle rollers.
open its breathing and lower its reciprocating top end mass with some lighter titanium valves, springs and caps etc.
Me thinks I better calm down, before I join the list of bidders