Steve,
If you still have your order from MAR-K, check the part number. Mine is #120187 (smooth with tag box). They also sell what they call a "full height" pan #120210 (smooth with tag box).

The catalog says the tag box goes below the rear sill (for #120210) and the part of the pan that mounts to the sill is only the thickness of the sheet metal so it lays perfectly flush. If this is what you have, then ignore all my ramblings thus far.

Mine sticks out (as shown in the sketch) and the ends are fitted with triangular pieces spot welded in place. Take a look at their catalog to verify which one you have.

Good Luck!