But regardless of what the fendertag and build sheet show, the pedal assembly could've been swapped.
Here is a manual-brake C-body with a power brake retrofit, using the original manual-brake pedal setup. There are extra lever-brackets to reduce the throw on the pedal, which spaces the booster out from the firewall. (this is not very common on a C-body, as I believe it was a field-retrofit thing)
In this pic below I've sketched how to identify a PB from an MB. (this is a Fusey clutch pedal setup but the other principles apply)
The upper red circle would be a pivot pin.
The lower red would be the pin where the power brake booster rod attaches.
The blue circle represents where a manual brake would attach to the master cylinder.
If the rod out to the brakes attaches about 3" or so down from the pivot pin - it's a MB pedal.
If the rod attaches like 5-6" away - it's for power brakes.
As the pedal needs to be in approx the same location for the driver, the bracketry for the power brakes is generally taller to get the pivot pin higher up.
It's all a matter of proper leverage for the driver's leg. The power-brake system doesn't need as much leverage.