If you go wider then a 235 60R 14 you may need to keep those truck bed fenders off the rubber because the wheel well can't take much more then that.
I went as far as I could go with a stock diameter and pretty sure they are 7in. rims I used on a lowered 2 inch block rear and cut coil front cassis.

These images sort of show the spacing. This was the direction I went though with higher profile tires so the speedometer stayed in check. You could go low profile with a taller rim to compensate the short profile. You want to try and maintain your correct MPH readings unless you know how to re-calibrate a speedometer.
Front

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