Well since Brockway was bought by Mack.
Maybe this is the reason why the Mack C600 also had swing out fenders.
or at least the ones on mine do
expand the photo and you can see the hinges
1958 Brockway truck swing out maintenance fenders - photo-20201015_163415mk.jpg
just remove these 3 bolts and the fender swings out of the way
1958 Brockway truck swing out maintenance fenders - photo-20201015_163431mk.jpg
I used to own an 800 Dodge with nearly the same set up