[leegreen]

If you tapped the cover and the block you will never be able to pull it tight, you need to drill the cover slightly oversize so it can pull tight. Use a drill stop or eyeball it but that hole needs to be bigger than the threads on the bolt

Sounds like dropping the pan is going to be required one way or another. You could consider doing that first, properly tap those holes or just drill them out and put on nuts from inside. Then put the pan back and fire it up to check the leak. Worse case you have to drop the pan a second time if you go the nut route - can see why tapping the block is attractive.
But you have a hoist right? And a spacious clean shop if your pictures are accurate - I am green with jealousy!

There are some tricks you can use to try and keep all the threading swarf from falling into the hole. I'm not sure I'd be confident enough to risk it with a bypass filter or no filter at all? and a valuable engine.