273 Rockers

scatpackbee said
My factory 273 adjustable rocker arms and shafts that are on my 340 do not have the banana grooves on the shafts.

They must be ‘64 assemblies…?

Probably. I'm not sure when they started exactly. The '64's I've seen didn't have them, but, my '65's did. Maybe late '64 Or early '65 is when the change was made.