I have been here before, 360 magnum, over 200,000 mikes, ran perfect, cam bearings all looked like that. I noticed they beat out of the block very hard, the new ones went in like any normal engine. The cam turned with my fingers with new bearings. I think it was caused by stress/fatigue/ dirt/burrs on original install. The rod bearings were also down to copper. The oil passages in the block were already bigger than old small blocks, other than 1 behind the oil filter. I don't think your oil or towing was the issue, just fatigued at install, from what I could see.