It's a tapers TRE hole, so its alot narrower at the top.
A rat tail file is going to take way too long to drill it out. When I did mine I had the same dilemna, I had the bit but my drill was too small. I ended up putting a dremel grinding stone in the drill and it still took a long ass time to get it ground out.
In the end, I wheel pretty often, and I wish I woulda went with the extreme duty. Having a double shear mounting point would've been way better.
Make sure you tighten the ever living shiiiiit outta that track bar. Then in a few days tighten it again. The bolt will stretch, so the re-tighten is crucial. If you dont, you'll start noticing after about a week that theres a crunching noise when you steer. That means the track bar is loose, and what you're hearing it the threads on the trackbar bolt grinding around in the hole of the bracket.