It looks like they state it can be taken from 904cc to 944cc - there it can be easily to chipped, gain 12hp? Sounds possible. Not really a small job, I guess you're talking at least some head work?.. I'd possibly want to rebuild the whole motor though. ££££'s
Didn't they have small 750 type heads and also small valves and tame cams. Sure they were quite lowly tuned from new.