I had two IRS setups in mind with the polaris FNR. The first was pretty much what i have, trailing arms with chain drive and a pivot point jackshaft. The second uses a little more real estate lengthwise. Engine driving FNR, FNR driving a carrier hub right behind or under it with CVs. could be dual a-arm or trailing arm setup with that configuration and there are several zero-plunge builds out there to copy the a-arm geometry from.
A couple years back 3 or 4 of us on here kicked around the same idea you've been pondering and just couldn't come up with any reliable and simple way to get around the twist. It's a driveshaft type configuration ... unless you invent some spherical ball link chain.
