I think the best option for the rear is 19.5" wheels. You'll need wheel studs that are long enough for both wheels. For the front, you can either change out the hubs or use the extenders you mentioned. Beware that most, maybe all of the extenders on the market are for 5/8" studs. That might be okay but I don't know. You'll need flat nuts for both front and rear or use the tapered nuts with the taper turned out. You might post in the parts wanted area for someone to trade front hubs with you because there are always people wanting to change from dually to single wheels.
