It is highly advisable to have same size wheels and same size tyres (lost count of how many times this has been said!). It is possible to have different size tyres, but they will likely be different brand / style between front and back. There's a lot of stuffing around working out and matching rolling diameters.
Same size tyres on different width rims might have different rolling diameters.
The advantage of all rims same size is you can swap front <-> back to even out tyre wear.
The ATTESSA clutch is in the transfer case, on the side of the gearbox.