Diy - Magnum Swap!!
(Covering this again for other people even though we talked about it on FB)
I've done 2 of these Magnum swaps now and have used the 1 piece oil pan seal with no problems + no trimming of any sorts on any gaskets/seals on both of my Magnum swaps, serpentine or V belt. Come to think of it I do believe having somewhat of the same problem you're having, but then found out it fixes itself perfectly in place by stretching as you begin to bolt it to the motor. Maybe they make 2 different one piece seals, maybe it's something to do with your oil pan, or maybe as I said it just needs a little help by being bolted on/having it stretch. Remember to use RTV in the corners of the front and rear main bearing caps after you've figured out if that seal will work for you.
Thanks! I love these air cleaners to death as well. Yes I'm trying to be very particulate and get every detail I possibly can on here for future reference + to help others :). Finishing my 2nd Magnum swap and did the same as before with the RTV on the front & rear of the intake, absolutely no leaks. You can use those gaskets if you want but I'm just going off of what I've found out and know that works. I'm also constantly updating & editing this thread so give it a refresh every now and again, hope that seal works out on your oil pan!