Can this be repaired?

Cudahemi is right. If you can find a good welder that knows cast iron it can be welded. But another problem is if you don't know the guy well he may charge you as much or more than a bare block will cost you. Around me welders don't touch cast for under $100 because of the time involved in welding it. First the cracks have to be drilled out at each end to prevent further cracking and then the block heated up then welded then somehow very slowly cooled down. That's best done in an oven. As far as tapping it out bigger it looks like it's cracked really far from the hole and the raised support area is completely cracked. In my opinion just from the looks in the pics I wouldn't try tapping it out bigger. One other option you have and what I'd do is have it completely welded shut and use the large fitting in the center for the oil input from the filter as it goes to the same port as the damaged hole.