My rims are 700c so new brakes shouldn't be an issue. I can brake from the top of the hoods but as they are quite stiff I can't get much power so if I want to brake hard I have to change riding position. I'm hoping not to have drill anything - I went to cycle surgery to get a new rear tyre and the guy said a new brake should just screw in where the old one is easy.

I think the currently fitted brakes where quite high-end at the time but their single-pivot design would probably put it at a disadvantage to even cheap dual-pivot designs..

Just found all the parts list:

Rigida Rims, Malard France Hubs , Stainless Spokes,
Atax Franco Italia Bars And Stem
Simplex Gear Levers ,
Simplex France Front And Rear Derailier
Fluted Seat Post
Weinmann Brakes
Selle Italia Seat

PS extra pic: