I've had a few sets of the frame braces (various mfg'r) on different year model Chevelles including my presently owned '67.
Never any issues with exhaust systems...either with stock OEM type replacement mufflers/tails, 3" custom mandrel bent systems, or aftermarket performance (Pypes) kits.
Plenty of room.
EDIT: Found a pic on another post that just so happens to show a great view of the braces and their position in relation to the exhaust system.
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