Only significant difference is length of jockey wheel bolts, and the thickness of the jockeys themselves.
I've run 9-speed mechs with 8-speed ergos, and vice-versa with no problems. You may find a little more chain-noise when crossing the chain, but that should be about it....
Completed: 94 Stumpjumper w. M733; ; 92 Dave Yates 731 ; 97 Parkpre Pro-Elite ; Pace RC200 F6 ; Pace RC300; 82 Gios Super Record ; 97-8 De Rosa Giro D´Italia; ; Banani SPX Track bike ; 89 Alan/Mavic Cross Bike ; 05 Focus Cross Team ; 90 Look MI-80 all-Mavic ; 12 Focus Izalco Team/custom build ; 11 Focus Thunder Custom build
Projects : , Brouwer all-Mavic
Stripped : Pace RC303
Gone : GT Karakoram
Stayed in the family: Kuota Kharma, 04 Stumpjumper FSR
Ceased to be : Dynatech MT3, killed by corroded seatstays.