domningo, we used 2x3" .100 thickness rectangle tube when we did the connectors in my brother's 66 charger. We slotted the front part of the rear sub-frame so the connectors would slide inside, then welded it all back up solid. They don't look like they protrude through the floor much more than yours. Same deal where once you trim away the insulation under the carpet on top of the connectors, you don't know they're there. We just butted the connectors up to the torsion bar crossmember and welded them together instead of notching it like you did.

Before/after difference is night and day. Before if we lifted one corner up with the floor jack, the doors would open/close very poorly. Now with one corner up they open/close like it was on all 4's.