Look at the water pump again. It's a short-shaft but the low-mounted style of 55-2nd and later. The valve cover is 4-screw and has the vent slots. It has lots of chrome/bling, and an altrnator - all non-original for 54.
The stamped serial number behind the distributor is the best way to tell.
Which won't really hurt the value at all, unless it's a trailer queen truck.
