I have a 12" C-man & a 14" Grizzly w/riser block I have always used the 80" recommended blade length for the C-man & the 105" recommend blade length for the Grizzly with no problems. I would go with the factory recommended length blade. It should be in your manual or you should be able to get a copy of the manual on line.
"Forget the flat stuff slap something on the spinny thing and lets go, we're burning daylight" Bart Leetch
"If it ain't round you may be a knuckle dragger""Turners drag their nuckles too, they just do it at a higher RPM"Bart