Tim,
The 54/55 panel-body tank is different from the earlier Advance-Design panel tank. Also, the 54/55-1st mounting straps are different from the 47-53 mounting brackets. I spoke with Mike about this when JC was having the tanks made, and I spoke with Mike about this yesterday.
As I posted above, I think the 47-53 tank can work in a 54/55-1st panel-body truck (using the different/new 54/55-1st combined ("integral") fuel-gauge-sender/fuel-feed-line. I did not mention that the mounting hardware also differs - the earlier brackets will not work on the 54/55-1st panel body trucks.
Here is a photo of the tank and mounting pieces in a 54/55-1st panel-body truck and a discussion of the differences compared to earlier fuel tanks:
http://1954advance-design.com/Documents/EngineeringFeatures/slides/orig_Page52.htmlTim
