Shift levers, as Sreten noted, have always been rear on right side/ front on left, whether downtube, brifter, stem, top tube, or bar mounted, the only exception I can recall being the Schwinn Krate bikes (e.g. Orange, Apple) and their copies which had those automobile shifter inspired toptube shifters, but even most of those, though centerally located, had their grips positioned for right handed use.