Finned vs smooth brake drum

I think any extra won't hurt for sure. So to get this straight, are you saying you could not upgrade to safer larger drum or even disc brakes because it's somehow "against the law"?

Yeah, basically. When you register a car here as a "historic vehicle" it has to be pretty much as it left the factory, or at least could have done. So as a Dart was available only with 9" drum brakes in 1963, that's what I'm stuck with. They also told me I have to get rid of the back seat belts which I just stuck under the seat and pulled them back again later. And I had to get a special certificate (and pay some extra, of course) to get an approval for 185R13 radial tyres as the only option in 1963 was 6.50-13 tyres.
The reason for "historic" registration is you only need an inspection every 5 years, no emissions regulations and the insurance is very cheap.