Thanks for the pics Billy----that is a bad design on the mounts and the only way you will stop the breakage is to turn those two steel mounts into a crossmember by running a tube down and under the pan from one side to the other--

As you have it you probably have a 20to1 leverage on the bolts plus in addition to the engine weight throw in the torque from the engine plus twist of chassis----your lucky the bolts broke instead of pulling the side of the block/waterjacket open----------

you could also shorten them and weld a mount to the inside of your frame rail so the mounts didn't have so much leverage against the bolts