Hi,
there is mention in this thread of B5's and G5's. I think the frame around the seat mounts is slightly different in each case, and different again from the C5. My account is of fitting a single seat to my G5 ('Electra' in the UK).
The front seat of my bike is the "Lycette" style one from Hitchcocks (part no. 91420), and it is really comfy. I don't think I sit too high on it, but it does feel significantly different from the original bench seat.
If you just replace the bench seat with a single one, then the electric gubbins are exposed to the elements. There is cover available from Hitchcocks (part no. 93086), which is has some louvres in the top (I guess to allow heat or fumes to escape from the battery, and is the right shape to sit between the frame tubes as they taper toward the petrol tank. The covers come in polypropylene or metal, and are secured with a couple of ziplock cable ties. I don't think you *have* to fit the cover when you ditch the bench seat, as the Hitchcocks catalogue doesn't seem to indicate that. However, things look much tidier with it fitted.
The rear solo sit sits higher than the front on the electra. This is because the available solo pillion seat has to sit on a small rack - and doesn't fit directly to the frame. Having said that, the rack looks pretty cool on its own, so at some point I might just remove the solo pillion seat and store it away for a while.
The one problem I hit was with the seat mounting brackets that run from the 'outboard' side of the rear mudguard carrier studs to the 'inboard' top of the rear shock mounts. There is very little thread showing on the 'outboard' end of mudguard carrier studs, and the nuts on the 'outboard' end are only half thickness (not many threads anyway). Once you offer up the bracket that supports the seat spring on each side, there isn't enough thread left to securely re-fit the narrow nuts. Luckily, there is sufficient spare length on the 'inboard' side of these studs to loosen off the 'inboard' retaining nuts and shift things outwards 4mm or so, to get the seat brackets securely fitted. Note that the studs were a *very* tight interference fit in the frame itself, and it took a while to ease them outwards the necessary distance.
Longer top shock mount bolts are provided with the seat to accommodate the thickness of the seat mounts, so these replaced the originals.