in my experience with a number of 55-59 trucks, the only difference in the frames is the 58/9 is about 2" longer to accomodate the splash pan behind the bumper ....
marked here on the 58 frame that I used to assemble a 56 cab and 57 front end, using rad mounts in the original position from the 58 frame -
fit fine .... I believe the carriage bolt type hardware was the earliest [55]
where you may be finding differences is in the V8/6cyl mountings - the V8 moved the core support toward the cab, back to the place where there's a triangular flat on the inner with a spot welded reinforcement on the 5-7 ... the assembly manual really only applies to 55, as they didn't print later editions incorporating running changes
Bill
