McCauley 73/51 1-A-90

No, that isn't a legal prop for a C-85. Sounds like the engine had been a C-75 and was upgraded to a C-85. The maximum length of a C-85 pop is 71" and the minimum length is 69.5". I'm pretty certain my prop was a 73/51 when my engine was a C-75. You can have it cut, repitched and overhauled at a prop shop.