Well, I've heard of people managing to get 31x10.50's in (which are the same size as 265/70R16) w/ no trimming at all and keeping the stock mudflaps, but honestly I just don't believe it. I think at full compression they'll still rub. I have 275/70R16's (BFG AT's) and I had to trim quite a bit (and my ARB rubs ) You could almost definitely run the Canadian mudflaps, though...

I don't really understand the "no modifying the vehicle" rule--it seems like if you're going to offroad your X (as evidenced by tire choice) you will be risking far greater modifications every time you go out (read: body damage.) But it's your call...in case you're concerned the trimming really isn't a big deal AT ALL.

p.s. What's up w/ the name...are you Pika's evil (or maybe good?) twin or something?