Actually, as can be seen here, the top of the side plate is cut to allow the sear safety to make contact, for the full recoil length of the receiver.
I have examined a Police pistol whose side plate was not cut out and it could be made to fit, but it was a real problem to install and I suspect that it was not original to the sear safety conversion (even though the side plate was number-matched to the gun).
--Dwight