What's wrong here?

My '72 750 didn't have a main/ignition switch when I acquired it. I purchased one from Andover (066395) however the switch is too wide to fit in. The part number is correct for this model. Has the previous owner modified the bracket that attaches to the air cleaner back plate or is this the wrong switch?
Thanks

Is that some kind of rubber bumper on the switch bracket? My 850 does not have anything like that.I suspect that is
your problem.Just not sure on a 750.
YING

Just a wild guess, maybe the air filter back plate (with bracket) is the early '68-'69 Commando type which had a narrower two-position Lucas S45 switch?

L.A.B. is correct you need the switch shown in his photo, My Fastback registered in 71 is a 70 model, it has this type of bracket and switch.