Any gains adding 1.6 rockers to stock 273?

Ok then why the heck did you even come and ask? You've got your mind already made up. When you spend 300 bucks and there's not one single detectible change, I'm sure you'll come on here bragging about how it has 500HP. We're just trying to save you 300 bucks for basically nothing. Go for it. You've made your mind up.
Getting kind of late
That is, IF the pushrod angle is optimal. Small block Mopar pushrod angle is anything BUT optimal. As a general rule, you lose about .020" of total lift regarding the terrible pushrod angle.
The way I see it, the 1:6 ratio helps that. AND the ball to cup conversion on the adjuster.