I have an old steel road frame I want to convert to a fixie. It has a standard horizontal dropout on the non-drive side but the drive-side dropout has a flat steel piece filling the rear half of the dropout which effectively turns it into a semi-vertical dropout with no horizontal play. I would like to get rid of this excess metal to turn this into a typical horizontal dropout like the other side. What's the best way? Drill with a cylindrical grinding bit? Jigsaw with some kind of metal-cutting blade? Frame is pretty junky so high-risk strategies are OK.