fivewindow........NO, don't guess. The ORIGINAL 9N PTO was 1-1/8, modern PTO's are 1-3/8's. Wanna guess what a 1-1/8 pto will do inside a 1-3/8??? ORC's are a NECESSARY device for brushhoggin'. Without the ORC, every time you clutch to slowdown for a corner, fencepost creekbank, irrigation canal, all that centrifugal force from them blades whirring will drive yer tractor forward into them hazards.
BTW, ORC's come in 4-varities, will perform step-up and step-down sizing automatically. ALSO you will need to shorten BOTH brushhog driveshafts. They are made to be cut with hacksaw or angle cutter. You can use oxy-acetylene torch iff'n you want but will haffta clean-up the scarf. .........Dell, yer ORC safety preacher