If at all possible leave the 1511 number visible. It adds to the car's history. It's up under the roof above the door and will not detract from the restoration.
When rebuilding/restoring RGS business car Rico at the CRRM, after removing a layer of "tuscan" red paint we found a layer of Pullman green paint over the door of the parlor end of the car. Printed in gilt paint was a repaint abbreviation and a 1918 date. This coincides with the Railroad Administration mandate that all passenger equipment would be painted "Pullman Green" We left a small rectangle of green containing the lettering and framed it with a small frame from a file cabinet. It adds to the car's history and does not detract from the car's recent restoration.