look under the right rear wheel. That is where the brake is. There is a stopper on the shaft that moves fwd and back as you press the pedal. Have someone press and release to find what is stopping. Maybe the stopper is way back so there is very little travel to press the brake. On mine, the brake pad\block wore out so maybe someone fiddled with yours to compensate a worn block. Just guessing.
"sucker for old stuff" I hear you. I started big with 90's mowers when i started fiddling but sold them as i found 80's (i also have 70's/80's Snappers as u can see). Now pushing 70's mower and trimmer wise, most everything i own was made by my 6th birthday.