I have a very high SN'd H grade Lefever with an Infallible trigger. This gun was probably one of the Ithaca finished guns & I have no idea if the trigger was installed at Ithaca or if an after-market installation, but I suspect at Ithaca. It is just as 8-Bore mentioned with the little selector slide set into a notch in left of tang. One feature of these triggers is they simply alternate bbls unless the selector is manually changed & do not re-set to a given bbl on opening the gun. The selector itself slides with each pull of the trigger.
