Like others have already said, Cateye has made good bike computers since the beginning of time (but still well after your SS was made). You pick a model based on the size of the unit and the features you want.

I've gone back to using Cateye computers again after having several Garmin models. I didn't want to be bothered making sure they were charged up ready to go anytime I wanted to go for a ride.

When I did a tour of Vermont on my Super Sport with my cousin on his Super Sport in 1966, we kept track of our miles on a little odometer located on the fork near the hub on the front wheel. It worked by having a little spoke like thing attached to the bike wheel that rotated a star shaped wheel on the odometer. It went click, click, click making that gentle sound with each wheel revolution. Does anybody have a picture of one of these things? Or remember how made them?

Also period correct to your SS is a cable speedometer and odometer that had an attachment on the wheel that turned the cable inside the housing going to the speedometer. I think I had one of those on my 10 speed that predated my '65 SS. .