My experience is that in many 58 and 59 3100's, the brake line feeding the rear brakes is run down the left (drivers) side which was apparently a change from 55.2 thru 57 in which that line was run down the right (passengers) side. Again, from my experience & I have worked with several.
Delky Dave in WYO


1957, 3100, v8
2016 gmc 4wd