One detail many modelers miss is a dipstick on the top of the oil bunker. A short piece of tubing with a diesel lift ring glued in the top simulates this very well. If there are ashpan details along the bottom edge of the firebox sides, they should be removed. On the fireman's side, a piece of wire with a 90 degree bend in it, and attached near the bottom edge of the firebox can simulate the oil line that delivers fuel to the burner at the front of the firebox. If there is room for it, the Cal Scale oil line heater part is a nice added touch.
Tom