>>1602241with a really old frame like that pic you may need some adapters to fit modern derailleurs
there are three kinds of fitting
band on, used for very cheep parts or where oval tubes are present
clamp on, common on cheep and old bikes, only works with round tubes and each clamp is rated for a given outer diameter of tube .ie 28,6mm or 31,8mm or 34,9mm
braze on, used on old high end bikes and also on more recent frames with oval seat tubes
the shifters suited to modern derailleurs will require a given diameter of handle bar,
you may need to swap the stem in order to fit a suitable handle bar, given most handle bars have a larger diameter where they are clamped to the stem
also some old bikes have band on cable stops or band on mounted shifters
