If it still shows cross hatch marks, its a low miler. If you have carbon on top of the pistons, you probably have carbon in the ring lands and the rings are stuck. Since you have it apart, I would put on try a set of cast iron rings. A 250 can easily be over carbureted with a 4 barrel which will cause it to accelerate like crap and build up carbon from too much fuel. You don't need a 4 barrel on a 1946 2 ton. With the correct carb, it will probably run good.