Male: APLA mount base from ALPA extension tube set
Female: C/Y mount from a broken Yashica FR II cam
glued together with spring back for secure mounting

Somehow the C/Y mount base exactly fits into the step-up ring
luckily, and you do not need to file the ring to focus to infinity.
Of course you can make a similar thing for another cam mount,
this is my reason to have bought an SB for ALPA mount lenses.

I can mount this one on Speed Booster for ALPA mount lenses,
and infinity focus is available for Contax/Yashica mount lenses,
however it goes to very slightly over-INF, no mount stopper thou.
It costs me ALPA mount base $15 and a step-up ring for $1.99,
so I can use C/Y lenses on SB without buying an another one. :)