That's easy. That short N97X serial number was made in 1969 when S&W started using the N prefix.
For the rust on your triggerguard, soak the area in Kroil penetrating oil for an hour or so to loosen the rust. To remove it, use a copper Chore-boy brand scrubber pad to remove the rust. The copper is soft enough it won't hurt the finish. You may have a bare metal spot when done but you can either touch it up or keep it well oiled.
BillCA in CA (Unfortunately)