thanks malkin.
judging by the tinfoil measurement i did earlier, my sit bones seem to be around 5.5"-6" (140mm-152.4mm) apart, from their center areas. if i got a more standard 175mm wide saddle, i'd still have a cm or so of wiggle room on either side of the sit bones.
however--another question for anyone who might know--how far in from the edge of a brooks saddle are the "cantle plates"? not entirely sure whether i'd be cutting it too close with a 175mm saddle.