I ran into a glitch in rehabing an old park bench. The wooden slats were rotted out, so I'm saving the wrought iron end frames and fitting them with new poplar slats. I included a mid-project picture below of one of the end frames. I don't know if you can notice from the picture, the holes in the frame for mounting the slats were not in a straight line, but rather haphazardly. So each board needs to be custom-drilled to match the mounting holes in the frames. Problem is, I originally measured the distance between the bolts on one of the old slats and used that measurement to drill ALL the new (expensive) hardwood boards. I had made the careless assumption that the holes in the frames would be in a straight line. Never assume good workmanship! After drilling the slats, I applied about 5 coats of clear urethane spar varnish. The new slats look supreme, and I don't want to zorkk them up by drilling a second hole in each board to match the stupid end frames. So the only way out of the quagmire I can see is to drill the frame to match the boards. OK! Problem is, most of the new holes in the frames would intersect the old holes, and I know that drilling an intersecting hole is problematic, especially in 3/16" steel. So I need advice on how to stretch holes in steel into an oval shape. I'm thinking some sort of router bit, or a grinding bit that I could use with a hand drill. Suggestions? Thanks.