Any gains adding 1.6 rockers to stock 273?

As I said early on in this thread, you are unlikely to feel the difference going to 1.6 rockers.
There is NO guarantee that you will feel the difference. Nor is there any guarantee that you will get a 0.030" increase in valve lift. This is because rockers actually vary in design & actual measured lift. David Vizard comprehensively tested a variety of rocker arms in his BBC book. All were supposed to be 1.7 ratio. Actual measured valve lift varied from 0.555" to 0.636".