I dont think this is an issue of handle bar rotation. Vintage brakes levers and modern levers fit differently onto the handlebars. In addition, modern handlebars and vintage handlebars are bent differently.

Modern levers and handlebars are designed so that the lever sits flush with the top of the curve. This is because modern riding has evolved to ride more on the brake levers than in the drops. In addition, modern bars have a sharper curve, which allows brake levers to be mounted flush with the bar.

Vintage levers and handlebars were not designed with the same considerations. The vintage brake lever kinda just sits in the middle of the curve. Perhaps people rode in the drops more often, or just put up with the uncomfortable hand position.

With those two pictures, notice that even though the modern bike has the brake lever at the top of the handlebars, it is still much lower than the vintage bike. The modern bike has a way more aggressive position.

If you do not care about being 100% vintage, I would suggest getting some modern brake levers. They make the ride ALOT more comfortable. The tektro R200a are very retro shaped, and are very comfortable (and cheap!). They will not only raise your riding position, but they also have a lot more surface area, so they will reduce the pressure on your hands. Also, most importantly (to me) they are much more rigid, so they increase braking power, making it much safer.