With a Leica II, as a general historical note, the most common lenses available back in 1931-32 would have been LTM lenses in standardized mounts:
Elmar 50
Hektor 50
Elmar 90 (Fat)
Elmar 135
Hektor 28 / 6,3 (?)
It was probably fairly rare to buy a new leica body then send your old Leica fixed-lens body back to the haev the glass extracted and remounted in LTM... this might have happened, perhaps Leitz offered some attractive trade-on deals...
I have a Leica II, # 77xxx with 50 Elmar nickel #99xxx, 11 o'clock Inf lock. I have also accumulated a black Elmar 90, a couple of black Hektor 135s and a black Elmar 135 (uncoupled)...
Just my two cents-worth...
Perhaps back before the War, it was reasonably affordable to have lenses "hacked" and remounted ?
Regards,
Luddite Frank