Hopefully an Irwin owner can say for sure, but by taking some simple measurements, and checking the shaft alignment with the rudder you should be able to determine what's necessary. If the rudder is 'in the way' than you'll need as much distance between the strut/cutlass and the rudder as the shaft is long.
On many raked spade rudders they may well create enough clearance when turned fully to one side.... On our last boat I could change the shaft, it slid by the rudder blade but only if the prop was off....
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"