Ugh, another broken mount. Poly-Locs?

I like the style of motor mount you showed. I used a very similar "Muscle Mount" on my 340 'Cuda. If you need some additonal strength you can always fab up a piece of metal and weld it to the motor mount that would also allow you to use the mid engine truck mounts on your magnum. That would reduce the fex from having the K frame mounting point so far away from the engine attachment point.

Just a thought