2+2GT

Depends what you're bolting to. If the bolts are passing through the front or rear frame rails, you'll crush them before getting enough torque on the bolts to stiffen the chassis. Really, 25 ft-lbs would crush the rails, nowhere near enough for a tight attachment. Get the strongest connectors you can find, and have them welded on. Anything else is just dress-up to impress people at cruise night. Don't think of welding as permanent. If you later decide to make the car a trailered show car, removing connectors will be the least of it.

The ultimate is to install the inner rockers and torque boxes like the convertible had. And most expensive. If I were racing, I would do this.