pulling the cage back is used for more than just carb location issues. adding volume in the case is one reason a guy might use a spacer. another reason is plenty of cylinders have the boost port shrouded by the stoppers. un covering the boost is generally not a bad thing. whether or not you see any gain from a spacer is hard to say. alot of variables involved and without testing it would be  difficult to guess. im sure jerry hall is probly the only guy around here thats messed with this kind of stuff