I did this !! Yes, I really am that old and sad........!!
I have built and raced slot boats, as a member of the club I belonged to at that time. 1967 would be about right, I had been racing for a couple of years by then, and recall dismembering a Revell 1/24 car to get the 36D motor to use in a boat.
The Enfield and District Model Engineering Society (EDMES) built a track or whatever you could call it, and one of the members made a mould for fibreglass hulls. 36D's were the motor of choice for most people, and the guide was attached to a spring-loaded arm similar to a trolley bus. They used to go quite fast if my memory is correct, and I remember boats being ballasted to set the trim and handling.
Most members built a boat, but the track wasn't used very much except for exhibitions and shows that the club attended. The Enfield Show was the obvious one, but I recall others including Dagenham and South London somewhere. I don't actually recall the Model Engineer Exhibition (maybe I didn't attend that one) but I do remember that club track being a very similar kidney shape to the one pictured.
EDMES got up to all sorts of other strange things, but those stories can wait for another time........