Don't the 3rd gen trucks have longer stock rears than the 2nd gens  ? If this is true like I think it is, then double check your rear spring lengths between the stocks and the chevies and adjust accordingly to keep your axle center in the stock location by comparing lengths from spring eye center to center pin location at both ends of the springs (chevies are centered and toys are offset).
  I thought I read somewhere also that 3rd gens are located like 9.5 or 10 inches forward as you mentioned but you'll have to do some measuring for sure. Measure twice weld once. Maybe this will help...