I'm left questioning what you're using for bolts Billy. Assuming that your motor has 2 bolts each side that fasten the mount to the block... Were they grade 8 or 5 or???

I used mounts for a "79" F-150 pickup, then a simple rectangular box from the frame of 3/8" flat stock with a angled end at the motor side, tack welded together with all parts in place \ mocked up. Then removed to bench for final welding. Then back into car for final assembly.

Because I had access to them from work, I used Bowman "Bowmalloy" bolts. They are like equal to a grade 10 or 12 or something crazy like that. I think the block would break before the bolts but at a minimum I would've used a grade 8 bolt.

I think the real secret is to do the mockup and fitment so that there are no undue stresses so that the mount only has to carry the motor weight and torsional force, any extra stress like twisting\bending because of poor fitment will surely shorten the fasteners lifespan.