i think the C stands for commercial.i think the C model had a swept forward front axle a year before the H model did.im not sure of the other differences,it might have had less flash being a commercial model.
truckin 88....I just bought a 520 HC and I went to the local Wheel Horse dealer that has been in business it seems forever and he told me all that you have mentioned but also that the front spindles are built heavier. Good that you have a manual. I been trying to get one off the Toro site and keep coming up empty.
Garry, THANKS! Guess I just was not typing in the right combination of numbers and letters. I now have everthing there they offered. Yes I found out with some other info gleaned from this site that my 520 HC was a 1989 and not an 1988 like I thought. Again thanks!