You'd be correct. check attached
The 47-55 1st series passenger auxiliary seat (RPO 263) swiveled on 2 brackets, they were bolted in 2 spots.
1 bolt on top and 1 bolt on the front face of seat riser. Check attached

Is there a difference between RPO 390 & 390B
In the 47 salesman data book, RPO 390 For panel models, What is Garnish molding for side door windows? Chrome, stainless or paint.?

xfiles
Attachments
1947-55 1st panel truck seats (1).JPG (152.04 KB, 248 downloads)
Resto Pack 1947 Auxiliary Seat .jpg (138.53 KB, 261 downloads)
Resto Pack 1954 Auxiliary Seat .jpg (144.12 KB, 259 downloads)
1947-55 1st Aux Seat Bracket.jpg (246.21 KB, 229 downloads)

1954 Chevrolet 3105 Deluxe Panel Truck
w/Factory HYDRA-MATIC