Bob-
I have two SA Backups, one marked AMT and another marked OMC. What part of the gun, specifically, are you interested in?
I carried one, chamber loaded, as a backup for years, until I heard of an accident where a Backup fired while in a jacket pocket, and the jacket was hanging on a peg. Supposedly, there was a great temperature differential between outside and inside. The gradual warming of the gun allowed the sear to slip and the striker to fire the gun.
I believe the grip safety only stops the trigger movement, doesn't lock the sear. I haven't carried either one in many years.