I am really surprised this didn't kick up

You are trying the sub frames front and back together, and to the floor. Using thicker steel than the rockers are, which is essentially your framerail. This severely lessens body twist.

Ask anybody building a big block A, B, E body car if their car benefitted from this mod.

Look at pix of my 67 below. You tell me if this doesnt make sense to you from a stiffen it up standpoint. 2x3 box steel 1/8" thick. Front and rear torque boxes made from 1/8" steel plate.

Anybody who thinks that they can update everything to modern suspension and tires and not stiffen up the chassis and it will handle just fine is an ID10T. I like Tony's posts on YouTube, but he is more of a purist. Some of the cars he knocks for not being original this or that. Some of which, i would have no problem with. He was knocking a white 67 fastback cuda for stuff easily fixed or changed. I wouldent kick that out of my garage.

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