I used to have a 64 plymouth 4 speed street / strip car, no frame connectors or bar as it only ran 12.50's. When I got rid of that car there was not only cracks on the A pillar, I could stick my finger between the windshield and the A pillar because the body was twisted so much. On my 67 Barracuda , A pillars have cracked and the floor tunnel is twisted / buckled even with frame connectors and a 6 point bar. Also , most sheet meat on older cars were 20 gauge or less. 12 gauge is fairly thick, 10 gauge is 1/8".