So to answer the question, yes you can run a 9.5" wheel and 255's up front on a g-body.
BUT there are some issues that need to be addressed. This 9.5" wheel has 5.5" back spacing, that's pretty deep, and obviously that makes 4" width from the rotor outward. As you see them I have a 3/4" spacer behind them. This is a definite necessity, notice how close the rim is to the tie rod. It doesn't contact the wheel but it would probably knock off clip on weights.
Another problem area is that the tires would hit the rear side of the plastic inner fender wells in the area where the arrow is and would not allow them to turn all the way. Simply removing and/or modifying them will give the necessary clearance.
Here's the passenger side with the inner fender well removed and the wheels at full lock.
