If you go to Savage FAQs at the top of the forum there are some very good articles in History and in Catalogs you'll find scans of original catalogs covering the 110 back to 1961. In Cartridges of the Savage Model 110: 1958 - 1999 you'll find the .243 Winchester was introduced in 1959.

That's a cool old Balvar! Mine wears a Balvar as well, but about 16/17yrs newer than the rifle.

I'll pull mine out later today and post pics of the trigger. Will provide measurements as well. Know for sure it is grooved like yours.