Lewis Ting inquired about drilling bars for exit holes for bar end shifters.
I have drilled entry and exit holes for brake cables on a pair of Cinelli bars way back before period correct was even thought about, in 1985 when my old LeJeune was just considered an old bike. They are still happy. I would not do this with a bar that did not have a double layer near the clamp, but that is just me, I also made sure that everything had a happy radius and that the hole was angled for a smooth cable path. The extra jog the cable would need to take to enter the bars near the control would add friction I would not be interested in shifting against.
For Campagnolo bar end controls I would not drill the bars but would try the cables exiting the handlebar tape at a point near the brake lever clamp, looking to shorten the overall cable length and eliminate an extra bend. This assumes no handlebar bag will be fitted.
My first "adult" bike, a Bertin C-37 was fitted with Campagnolo bar end controls, the upgrade to down tube shifters a year later was happiness for me.
John Jorgensen
Torrance Ca