Dusters have lots of room in their stock form for lots of wheel/tire out back. With the right offset, I think you can get a 15x10 back there with a 295/60/15.
To answer your question re: the 14's, I think you could get a 245 on the rear and would be safe with a 225 on the front. Height-wise: Maybe 60's on the rear and 60's/70's on the front - depending on what you are looking for. Have you thought about going with 15s? Perhaps 15x8s out back & 15x6s in front.