If you really want to improve the handling, that is a good modification. Why not use a bolt in one? Those can be bolted in and/or welded. Easily removed and just a couple holes to seal up if you (or a future owner) wishes to remove it. I have a set and have two more on order from Magnum Force for my 1972 Charger and Duster. You can put them in at home and if you should remove them, you can resell them. No hacking up the floor pan or modifying stuff. They were made for guys like you that want a more original car.

https://www.magnumforce.com/tubular-subframe-connectors-b-body-mopar/p20