Fit and calibrate a cheap cycle computer. Easy.
If you are at altitude, I am sure you can tune your bike to compensate to a certain degree.
Gutless when compared to what? It is geared appropriately for its power. But you cannot compare it to a modern bike.
I have a 1982 R100 as well as my R65 and frankly, I do not know what all the fuss is about. Its poor handling (when compared to the R65) keeps the speed down on the open road, so any power advantage is a moot point. It is definately a 'rubber cow'. Its a standard R100 - naked. With Konis rear shocks and Euro bars.
I am considering beefing up the front end to make it more R65 like. But money keeps being diveted elsewhere
Steve H