There are no such animal as stock mounts for a hemi in a 1960 D100. The mounts I've made are much stiffer than any factory stuff and I also have a turnbuckle on the front drivers side just in case. I would have said it's not possible for what happened to happen but it did.
The slicks are old and to small. With a lot less horsepower this thing used to pick the front tires up and run some really impressive 60 ft. numbers for what it was. From looking at the tape the rear springs are past the limit of what they can control. I'm suprised they worked as well as they did for so long. They're only 50 years old now. Dave