Kudos to Tim at NFG (yeah, I wrote that) and John at Go Moto, here in Minneapolis! I now have the extra bracket needed to mount that Lycett seat on my C5, using the OEM seat springs and not the springs that came with the solo Lycett. When I get home on the 2nd, I'll swap the gel-padded Lycett for the OEM plank, put the Vista Cruise and the Hagon shocks on, and that should just about get Fiona all prepped for the run up to Sault Ste. Marie.
I'll try to shoot a couple of photos of the bracket & install job, if anyone's curious about it.