So everything I've run across pretty much confirms that 54mm is probably where you're gonna be stuck using the case you have. The bearings are actually the same bearings with the 56mm Mag case. They're just referred to as being 'included" with the later case assembly and part number, not different. The tech notes describe a variety of other items like air flow/filter setup and differences in the WJ4 carb for the Mag application, but the case change for the larger top end is the main consideration. Different spacings, larger fasteners, and more case material in the mounting surface to handle it all.
There's a lot of reading on the subject if you Google it. A couple guys say they've turned Supers into Magnums, no problem. Others have called BS on that.
While anything is possible, most would stick with the 54mm configuration with some minor port work and slight timing advance over trying to adapt the larger top end to the smaller case. Those who've run both will also claim the difference between a Super and a Mag doesn't become evident until running 36" plus setups in big wood anyway. I can say from personal experience that a well tuned 87cc Super with the multi-port muffler and a sharp chain is a pretty stout saw in its own right -- and that's up against my rather bad ass 066 flat top which is no slouch by any means.
Not exactly anything new here on the subject, but an interesting and fun refresher for me nonetheless.
Hope it helps.
