Re: Different sizes?
Try your absolute best to stick with a 100% match. Differences of 1% or so will probably be tolerated, but big differences (26" vs 30" tires) will cause big transfer case trouble.
If you're really into the bigs n littles thing, you could potentially mix and match tire size & gear ratios (front and rear) to make the transfer case happy. For example, a 26" front tire & 3.42 gears would work with 28.9" rears and 3.73 gears. Summit Racing's Quadraduece uses this kind of sizing scenario to make the tcase live & give the car "the stance".
'JustDreamin'