Re: Can a 3 way selector fit into a 5 way casing?
It depends on the switch in question, but there's no reason it shouldn't if you buy one roughly the same sort of design as the old one. A 5 way switch is just a 3 way with 2 extra detents. The first "5 way" switches on old stratocasters were 3 ways with matchsticks jammed in to stick them between two positions.
Things get more complicated if you've ordered a superswitch. Those are entirely different inside and are usually slightly larger as a result of the extra configuration possibilities. In most cases though, that still isn't an issue.