well I'm running a 75 duster, and I think I might be able to slide in a larger tire. We will see though. If it's not possible then so be it. I'm still a noob when it comes to a bodies.
On a Duster you will be able to fit a WIDER tire I am pretty sure. I don't know about a taller one. You should start a tread and ask the Duster guys what the biggest tire you can fit with a MINI TUB! I am sure you will find out quickly.