I agree as well. Unless I am mistaken, most mopar converter bolts are 7/16 by 20. This is roughly the equivelant of an 11mm thread size. Measure the depth of the hole and drill it out with a 7/16 drill bit marked with that depth, or a drill size based on the tap size you plan to use. I'd tap it for a 13mm threaded bolt (if you tap it for a 12mm bolt, you may not get deep enough new threads). You will have to dress the new bolt for head size and length as already mentioned.

Note: I have not done this myself, but it makes sense if you plan the tap and drill sizes well. Only possible problem I see is getting a dill in the right position with the oil pan so close! I'd use a mm bolt equalling grade 8, but grade 5 might also work.