The FX55 used to be called the "Super Distortion". Until some good lawyers from a pickup manufacturer started sending persuasive letters to DOD and they had to change the name.
Here are a couple of red rocking vintage DOD FX55-B pedals. The pedal on the left is probably from 1994. The pedal on the right is probably from 1988.
The left pedal has the "bar" style model name while the right has "box" style. The logo is "italics" on the left and is "shaded relief" on the right. Footswitch plate is blank on the left and has a "DOD" on the right.
Below shows some differences in the bottom plates. Smooth for the left and serrated (WICKED!!) on the right.
And on the inside? Not much difference. The PCB layout hasn't changed between models. The biggest difference seems to be a transition from yellow to greenie caps.
Both of these came into the repair shop with switching problems. Here's the internal switch on the 80's model.
Information on the dates of these red rockers came from the
America's Pedal web site.