A PS on the suggestions... the OE unibody was not really made for high handling loads. After 45 years maybe less so. Stiffening the chassis can really help along with upgraded suspension components. The more you push the suspension, the more benefit from stiffening. There is a long list of things that can be done in this area to help beefed suspension do its job.

First is welded in frame connectors which really help and the list goes on from there. Torque boxes, gusseted and full welded K, plated LCA's, T bar mount re-enforcement plates and more. I would suggest you at least start with the frame connectors. 2" x 2" box steel, 2" x 3" box steel, floor fitting stamped type they all help quite a bit. FWIW I run 2" x 2" box connectors made by ART (Auto Rust Technicians).