<guess>the above fork is more like the OP probably has .. I measure 6cm between the post centers on mine .
I have NL made Spooky cantilevers on it now .. a redesign of Mafacs .. I have Mafacs on another, older bike.
[pictured in 2nd, 4th, 9th post, post spacing is wider, a more common set up of late.. the CR 720 in OP would fit, there]
Shimano's new CX 70 may also work ..the pivot is offset towards the center ,
you can use thinner spacers under the brake shoe to make up for the width distance between pivot centers
Last edited by fietsbob; 08-23-14 at 08:25 AM.