Don,
Forgive us doubting Thomases. We are very used to people who have trucks about which they are sure everything is original (usually because they were told that by people in the family, or by the seller).
I was also going to chime in with a chuckle, but I first checked the 1947 Chevrolet Truck Data Book Advance-Design Models. This would have allowed me to assure you that no odd running-board option was available on 1947 3104 (1/2 ton pickup) trucks.
However, I am pleased to report that there was an Option No. 389 in 1947 for only the 3104 model: Wide Running Boards, " . . . ideal for newspaper or other types of jumper distribution." I'll try to scan a photo. The illustration does not show a seam, but it is not a photo and the artists took liberties back then.
Just chill out and smile smugly.
