I'm pretty sure buddy you just put a washer or two between the brace. That's what I seen most people do. Some cars it doesn't work for some reason though. You could always put different motor mounts in though.
My brace is just bolted on as factory. No washers or spacers. It fits just fine over my CJ manifold. Obviously less clearance than the factory Boss manifold but still plenty. Factory motor mounts and everything.