The left side ones have similar functions. The 550 ones might have a slightly different metal case, but electrically they work OK. The right one: if yours has the ON/OFF headlight switch, the post-1976 750 does not. On those, the headlight goes out during START from the START button, there is no HEADLIGHT OFF switch. If yours has no ON/OFF switch, they will plug together, although you might need to add a Black splitter in the headlight bucket to feed your headlight or the RUN/OFF switch (from another Black in the main harness). Some of the later 750 right sides had 2 Black feeding the right side, some only had 1. Same can be said for the 550. This Black circuit feeds both the headlight power and the spark coils (via that Run/Off switch - comes back as Black/White).