no load on the
roof at all - racks like that were mounted on the rain gutters, above the sidewall stiffeners and pillars [studs] - the gutter area has 3 interlocked layers: the roof stamping, the gutter itself, and the flanged side wall, making quite a sound "lam-beam top plate" .... wouldn't want to carry the whole GVW up there, but quite strong .... similar roof racks were very common in the day, originally wood cross bars then aluminum tubes, both with stamped metal clamp feet - sometimes they had suction cup feet that sat on the roof right at the curve with straps that secured to the gutter
when I hit the road with 2 friends in a 55 International panel, we used a pair of those racks supporting a sheet of 1/2" ply with a home made canvas cover over a whole bunch of our supplies and camping gear - climbed up the hood and over the windshield to accesses it, just need to tread carefully on the bendy sheet metal
Bill
