Big issues with BB mounts on Dart!

I'm assuming you used the bolts that came with the mounts on the block side of the bracket. There is supposed to be some movement in those to allow the brackets some adjustment to the block, they don't get tightened up til you have the engine positioned where you want. When you installed the engine did you drop it in maybe passenger side first then try to roll the drivers in? May try getting drivers in position first. Just some thoughts.