It's a bit of a crapshoot as to whether the body will fit.
I did some swapping a couple years ago, to turn a no name 7 speed hub to a 9 speed using the body off a FH-M570.
I'd recently purchased a couple FH-RM30's ($20 ea. delivered for the whole hub) and tried to swap the "no name 7 speed body" to one of them to reduce dish. It didn't fit.
One thing to check is the spacers. Sometimes the spacer material "extrudes" a bit around the rivet holes and has to be cleaned off with a file. Else it makes the spacers "wider" upon reassembly.