The ex mechanic in me would like to call attention to some practical considerations:
Option 1 - Down tube shifters, clamp on
The problem with this is that without a braze on stop tab, DT shifters have a strong tendency to migrate down the tube. They will need to be put on very tight, and this will destroy your paint job. An ugly modern clamp on adapter like the one problem solvers sells may hold better. I don't know. Already mentioned are the aesthetic considerations of having unused head tube stops just sitting there. Also, in case you care and FWIW, it isn't period correct. Clamp on shifters were phased out in the 70s.
Option 2 - Brifters
Main issue is that you will have to lose the SR derailleurs. At a minimum, you could go with Microshift 7 spd brifters, and replace the derailleurs with shimano compatible types. More likely, you'd be re-spacing the frame to 130, rebuilding or replacing the wheels, and going with 90s era campy brifters and derailleurs. That's a lot of work.