Cyclocross - brake options on old cx frame

hi everyone,
got this old gazelle frame and wanted to build it up as single speed. the problem is that the front cantilever sockets are only 5cm (c-c) apart from each other and have only one hole for the spring. had a similar frame a few years back and remember vaguely that i had a hart time finding brakes because modern frames seem to have more space between rim and cantie socked. would mini v brakes like the tektros work?
ps: the maximal allowed wide of a flat bar is 20" right?

any advice would be greatly appreciated, thanks

I don't know about the brakes however I don't think there's a flat bar width requirement.

I don't know if this helps but just put a pair of Tektro 926A Mini V-brakes on an old 1993 rigid MTB frame that I converted to a cyclocross style bike, and it worked (sort of.) I needed to stack a few spacers on the brake pad post to get the right amount of clearance for proper braking but eventually it worked.

Only 50mm apart? That can't be the center-to-center measurement can it? I just measured my bike and the rear was 80mm and the fork was 85mm. I have the Tektro rx-5 mini-V brake and set the pad holder washers up so the front pads are closer to the rim (to make up for that extra 5mm gap). One of the convex washers is thicker than the other so there is some adjustment there.

In your case, you'll either have to open the v-brakes up a lot more so that the brake arms won't be perfectly vertical when pads hit rim (vertical is optimal but they'll work regardless), or you can just use a canti brake and pad holders that will allow you to angle the pads correctly so they are square to the rim when they hit. See if you can borrow some brakes from someone first to make sure it'll work... If not, you may have to find some vintage cantis with the posts that allow you to pull the pads far back in towards the brake arm.

Period Brakes.. Mafac and Modolo cross, Cantilevers, from the 70's and 80's
work on my bikes,
Front Bosses .. they're on 6cm centers ..

Look for a TRP style brake that use the old post brake pads as said above. These would be great and inexpensive. They even have adjustable brake shoes so you can toe in.
http://www.velo-orange.com/grcrucabr.html

http://ep.yimg.com/ca/I/yhst-84224226242177_2124_32561733

thanks guys, tried a pair of the trp kind from a friend and they fit. so guess i use those and try the v brake if i come along a cheap one...