The major differences between the MS and SL as I understand them are aluminum shock bodies, external reservoirs (front), and significantly more adjustability. Obviously they are also rebuildable…not 100% sure if this is the case with SLs.
You can go with identical spring rates on either and I bet both make a marked difference in handling. So, for most people the MS is probably overkill and the SLs are perfect. Just my guess though.
And now the elitist comes out…again…pretty cool to pop the hood and show folks “hidden” external reservoirs.
I have never heard of anyone modifying the SLs to add reservoirs. I would surprised if you could do it and even so, highly doubt it would be cost effective vs. just buying the MS.