The OS is a beautiful machine indeed.
Where the SP/Magnum makes use of a basically "standard 90 fourstroke carb" that interchanges with any 90 single OS/ASP/Magnum, the OS 160 twin does not. The carb mount is different..
The ASP/Magnum make AFAIK (I never personally checked) use of standard bearing sizes, the OS, from what I know, uses a fairly hard to find odd size bearing at the forward crankthrow. Apparenly Boca can supply them. But also AFAIK that odd size bearing is odd in its width, so theoretically it is possible to fit a standard size with two filler rings. Not that I would want to recommend it, but in a pinch...

Running them both, side to side I could not determine any difference in power or behaviour between the OS and its cheaper counterpart, but the OS is way more beautifully made,