I have re-posted the photograph of the shaft damage. Please review the photograph carefully, It shows the the wear of the shaft. It was dark in the garage, so I could not get a better photograph.
The damage is substantial, 24/4ths of the key way is worn away.
some parts of the linkage are heavy duty, like the linkage that directly connects to the shaft, but other parts are merely rubber bushings. Not much mechanical advantage, simply linkage from the shaft to the operator's hand, plus some shock absorption to, I assume, make for a smoother transition from forward to reverse.
View attachment 581559
It looks like the key way is intact but the sidewall is missing. After disassembling the pump do you think you could weld the shaft up and turn it back smooth? What are the odds of locating a new part?