I just grabbed my lantern & went to the garage to inspect my 1981. No pop-out plug, though there's a plug at 0900 position on right side of drum (Allen wrench fitting, as the photos show.) No metal pointer, no scale, no line. Go figure.
willr65 said: << The R65 rear brake is as useful to stopping as a chocolate fireguard! >>
For emergency stopping, true. But that doesn't necessarily mean the rear brake is useless as a brake (as opposed to a brake light switch). The instructors in my Basic Riding Course mentioned that lightly using both steady throttle and the rear brake can enable tighter low-speed turns. Also, David Hough in one of his "Proficient Motorcycling" books advocates light use of the rear brake. OTOH, Lee Parks in "Total Control" says to use the rear brake rarely, perhaps never.
Hough goes into the physics of weight transfer, tire adhesion, and consequences of locking either rear or front wheel in great detail. His conclusion: be very careful with rear brake (more so than with front brake).
I'm a former bicycle rider, and putting more braking force, or relying solely on, the front brake is not instinctive to me. A good bicycle front brake can cause a "stoppie" in a heartbeat, and a 180-degree stoppie nearly as quickly (if not done correctly). I've had to learn a different braking technique for a motorcycle. The same goes with steering. Countersteering might work on a bicycle, but I've never done it. The light weight of the bicycle makes body-steering an effective technique. (I don't recall even hearing countersteering discussed by bicyclists.) Other bicycle techniques (e.g., counterweighting in low-speed turns and standing on pedals to lower the COG) work well on motorcycles in certain situations. Still, the techniques are different on the whole & require a bit of relearning to go from one to the other.