Drilling and/or welding on frame flanges is bad juju. It creates unwanted stress points that can lead to cracks. You can pretty much Swiss cheese the vertical part of a frame rail without compromising its strength, but stay away from the flanges. I'd recommend running the brake lines inside the C-channel wherever possible for maximum protection, or along the back side of the crossmember under the core support.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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