Hi
Mr Jones, 
on getting yourself a great score there....
For info on the squealing starter clutch...See Grumpy's post
HERE For the height adjuster and handlebar grips, they will be almost impossible to find unless someone is wrecking out one of these machines, as rubber parts of this age don't last long, particularly if the machine has been exposed to the elements.

Your Briggs 60112 was manufactured on the 20th September 1977, so your edger would be a 1978 model.
here's some details: