This cutting the huge percentage wise holes in the TB crossmember seems to ignore the main purpose of the crossmember's function, and effectively weakens it, to gain stiffness of the FC. The TB crossmeber is ALWAYS taking load, except when on jackstands or wheelstand when airborne. The FC does not. I would strongly suggest thinking this solution, at this scale (size of holes), over very carefully, as it is hard to reverse. I mentioned and others have mentioned alternative solutions.