As far as I remember the number part refers to dimensions, width etc. They were usually designated in groups with a prefix according to road/MTB, eyeletted?, double wall etc...
There was a guy selling an original set of bonty rolled ma40s on ebay a while back....
....but unfortunately I bought them!
Six metal tyre levers to get a porc onto them though, think that's why we stopped using them 'back in the day', not the most race friendly rim in the world (although still not as bad as a set of matrix mt aeros)