If you don't mind converting the GS to a low level exhaust then the RS system may well fit, though you would have to make an extension to the bracket supporting the end can. However, this might mean that the standard GS panniers won't fit, so you would need to check this if you use panniers.
I fitted the exhaust end can from an RT to my last GS so that I could fit Shad panniers on modified Shad pannier mounts. Your RS system would probably fit in a similar position on a GS, so the pictures below may give you an idea of whether it would be usable.
On my new GS I have fitted a GS exhaust to which I have had part of the link pipe section from a scrap RT exhaust welded in place of the original, so that it fits at a lower angle and allows me to continue to use the Shad panniers and mounts.
Alternatively if the Akrapovic comes with the link pipe separate to the end can rather than welded to it, then you may be able to buy a link pipe intended for the Akrapovic GS system if the end cans have similar fittings to their link pipes.