Banshy,
just took delivery of my '86 250 xc
Have checked the caliper measurements and the mounts on it are only 60mm center to center, it runs a single piston brembo unit, I don't know if husky went to a dual piston set up on the cr's in '87/'88 or not, that's one for the husky anoracks to answer.
2hrs later....... just had a look at the manual that came with the bike, which is for an '87 model and it clearly show's a twin pot caliper front brake, with the mounting bolt's much wider than mine.....I'd say that's what it came from.