Any gains adding 1.6 rockers to stock 273?

Back in the late sixties, I went with my Dad to Smitty's Speed Shop in Dayton, Ohio to discuss replacing the 361 in Dad's 62 Dodge with a 440. Smitty had a fairly new Valiant wagon, 273 automatic. Originally a two barrel, Smitty said it was too slow with the two barrel, so he swapped in a four barrel. Can't remember about the exhaust. But otherwise, it was totally stock. He was happy with how much better it ran with the four barrel.

I'd say ditching the two barrel for a four barrel would be the single biggest - and easiest - improvement. Especially at higher speeds.