Hey Tommy - On my truck, it seems like the braking is biased to the rear wheels. It has bigger drums in the rear than up front. I've never locked the fronts, but I had to stop hard once and even with a 1-ton pallet in the back and I locked up the rears. That was also when I had very old tires that seemed a bit hard.
Who knows what was done on these things in their 70+ year life time. Someone may have messed with the brakes on your truck at some point to bias them front (or someone messed with mine to bias them rear, haha ) who knows!
