[Xeen]

As far as width goes I recommend a 8" wheel on the front and a 9" to 9.5" wheel on the back anything wider and you will have to modify the stock inner fenders and wheel houses respectively.
As far as diameter you can go as big as 20" without modifying anything other than front spindles, CPP sells a modular 2" drop spindle that brings in the wheels 3/4" on both sides so that you can run disk brakes and retain the same geometry as the original drum brakes which allows you to run larger wheels.