There were a couple of different models of the standard old Weinmann "999 Vainqueur" center-pulls. The 610 had shorter reach arms (49-61mm) and the 750 had longer arms (57-75mm) - Those are the measurements from the middle of the central pivot bolt to the centers of the brake pads. Dia-Compes are basically identical. Perhaps that will help you calculate where the pads will hit your rims.

Remember, 700c rims are smaller than 27" rims. If you are using 700c rims, the brake pads will need to reach down 4mm lower than they would for a 27" rim. This also means you will "gain" 4mm of potential tire height when using a 700c wheel in the same frame, so it may help you with fender clearance... but just a tiny bit.

There was one problem people have had when fitting older Weinmann brake pads. One style was cut at an angle for use with rims with sloping sides - typically 1970s 27" chrome rims or smaller BMX rims had a slanted braking surface. There were also pads which were cut with a normal flat edge, and these will fit most moderate width flat sided rims. Dia-Compe still made the slant-cut pads (as of 2005) which were designated their "#76" style.

Weinmann actually still made their last flat-cut pads until just a few years ago. They were known as the "WX" pads. I believe they simply let their patent go on these, and subsequently a Taiwan company called Jagwire began producing their own identical copies of these which they call their "X-caliper" pads. Nothing fancy, but they fit perfectly and seem to work well. I've also seen "similar looking" pads made by another budget company (possibly "Pyramid"?) recently. But these are smaller overall and are really to be avoided. The better stuff measure around 40 x 14mm (around the metal holders) and will reach down around 18mm measuring from inside the caliper arm to the braking surface of the pad.

As for braking efficiency; I believe you will get more mechanical assist by using aero-style levers. I haven't had any problem stopping one of my Weinmann equipped commuter bikes in the crappiest of snow/rain weather conditions even using cheap-o pads. However, as John E suggested, the Kool Stop "Continental" pads with their grippy red compound are really superior to anything else.