What the heck!
Milodon has a problem. At $100+ for the pan it should fit perfectly and not have a leak issue.
The gap you are showing is WWWAAAAAYYYY too much. The Rubber should be MAYBE 1/8" longer than the pan. Not 1/2". This looks like a 318 pan trying to fit on a 360.
Get Mancini to replace it with a pan that fits. They may not even know there's a problem.
fastmopar