People racing with the C3 frame had a regime of gussets they would weld to the frame to strengthen it's torsonal strength. Many years ago, I had a bunch of stiff paper templates to use to cut out the steel to weld to the crossmembers...long lost. All of the crossmembers will benefit from gussets. Also, for frame strength you must add a spreader bar between the two front control towers to prevent the control towers flexing...and changing camber...during high g turns. Maybe it's my imagination, but with the spreader bars, I imagine the front of my 68 to be much more solid, even though I'm not doing high g turns!!