" why didn't the factory use them instead of torque boxes that tie the sub-frames to the rocker boxes? You see a lot of factory installed (on all makes) torque boxes on high H/P cars and convertibles, but rarely (if ever) do you see factory installed sub-frame connectors"

The factory relied on the rockers mainly, the convertables had a 1/4 inch steel box tube inside the rockers with torque boxs tied in for strength. But controled flexing kept these cars from breaking up to last 100,000 miles in normal driving. But if hammered on, with todays roads, connecters are needed

I believe the factory went to the unibody to make the cars lighter. And when they did that in the early 60's there were no tires that really hooked much at all so they most likely did not worry about it much. I know a pics of the Ramchargers 63 shows no rollbar and a 70 Pro Stock Duster I saw just had the little round rollbar behind the seat. I dont know if either had any type of frame connectors but I would have thought a 70 Hemi Pro Stock Duster would have been hard on the car chassis without any type of rollbar to stiffen the car and they were 4-speed cars.

I can say I ran my 63 once when first on the road with my old mid 11 second 440 in the car and after I put the connectors and 6 point rollbar in the et really did not pick up any which surprised me. Ron