I've been told that 3.55 ring and pinion sets may be available for Spridgets. This would seem to be a good alternative to installing a 5 speed or overdrive, IMHO.
The 3.55 gears would fit, but they're apparently rare. Probably could find some in the UK somewhere. These engines are fairly torqey and I don't think the reduced final drive ratio would be a problem. In fact, I'd love it. This would seem to be the way to go, IMHO. Cheaper than OD. Not easy to install, but certainly cheaper with the same or better reduction in RPM than OD.
Do any of youse guys have knowledge of the 3.55 gearset??