how about selling the zenit and adding whatever came of that sale
to your camea-kitty and then .. add a few more dollars to it
and get an m3, and use the lens you already have.
i have a me super and k1000 ( grand and great grandchildren of the spotamatic f ) great
cameras! but a greasy spoon compared the fine dining ( leica ) ..
the frame lines may be a little off, but i think you can figure it out after the first roll ..

have fun and good luck !