Definitely remove the crossbrace. No issues doing this with it off. For enlarging the holes, see my post below if you are using a Dremel, I found the perfect Dremel bit.
[QUOTE=370Zsteve;595476]A great tool for cutting the holes, the Dremel Carbide Cutting and Shaping Tool. Available at HD, Lowe's, any hardware store that carries Dremel stuff. It cut through the material like butter, and you can use it almost like a lathe as well as a cutter. Total cutting/shaping time: about 5 minutes per side. Cost was $16
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When re-tightening the crossbrace without a torque wrench, just tighten until snug (do not overdo it and strip a bolt or worse), then run the car thru some twisties for a bit and retighten. Better yet, buy a torque wrench!