I have a 1982 one and it has a dipstick, Joe, so that may be about when they made the change (much the same time as when they switched to Magnetron ignition). My 1982 one happens to be a 92508 though (Vacu-Jet carburetor instead of Pulsa-Jet), and by 1982 they had reduced the maximum governed speed of the vertical crankshaft engines to 3,000 rpm from 3,500.
I agree the dipstick is a better setup than the level plug on that engine. On some of the others the dipstick reached up so far it became a bit flimsy and vulnerable, but on the 92000 engines it was properly braced and just a better way to check the oil.
