If the issue is as I envision it, just pickup a piece of 3/4" wood dowel, wrap a piece of say 180 grit sanding paper around it, and then with some reasonable technique (important!), and in a barbers' pole twist & trust, including reversing the direction of motion, you should be able to "deburr" the oil gallery intrusion relatively simply. If the sum of material displacement within the bore is anything greater than that of just a "deburr" operation then the block should be taken to a proper machine shop, who has a proper honing mandrel (not a "ball-hone"!
) to square it up.
Oh, and that "proper honing mandrel", well, it costs significantly more than fifty-bucks!
Scott.