Very sharp! What years were the 3 speeds available? Do you know how the gearing is compared to the 5 speeds?
Stik Shift three speed bikes first appeared in August of 1966, and lasted until very early January in 1974. The gear range was 39-low, 51-normal, and 68 - high, used with a 14 tooth rear cog in the standard Stingray. I've seen reference to the following for 3 speed Sturmey Archer hubs:
Low gear - reduction of 25%
Normal Gear - direct drive
High gear - Increase of 33.5%
The best thing about three speeds is that there is no derailleur, so the chains don't slip off of the crank!
Thanks
Bob