From the look of things in your pix, the previous owner gets the cobble award of the year.
If it were me, I'd get the engine out anyway you can and replace the oil pan.
If it is an aluminum pan, put back in a cast iron pan, searching the internet like ebay or face plant it you do such, should be productive.
No telling how bad the bolt holes are wallowed out in that old pan and I highly doubt any tapping,helicoil or inserts will work.
Then go about repairing the frame properly, welding and careful grinding till it is like new.
