Subframe connectors/torque boxes question

70 Dart originally /6 now 360 magnum 500 plus hp. Ive ordered frame connectors. IIRC
Only 340 cars had torque boxes ??
If i do have torque boxes will They need strengthening ? If not can They be installed ?
Do I really need them.? Where can i get them ??

Performance builds and convertibles got the torque boxes. They tie the frame horns to the rocker rails so sort of like sub frame connectors just not a straight line. IMO If you're adding subframe connectors it doesn't matter if you have the torque boxes or not.

My numbers matching 1970 340 Dart doesn't have torque boxes, not all did, added subframe connectors, don't think torque boxes would add much more.

Subframe connectors and torque boxes act in different places and do different jobs. One does not replace the other. Torque boxes tie the frame rails to rockers, and box the leaf spring mounting area in the rear which increases torsional resistance. Probably more so than frame connectors alone. Which is why the factory used torque boxes but didn’t tie the frames together. They were designed to strengthen the corners of the box, which is why ‘verts got them.

That’s not to say that the addition of torque boxes eliminates the need for subframes either. They both can significantly improve chassis stiffness. Especially at the rear of the car where the torque boxes can spread the load of the subframe connectors out from just the rear rails.

I added subframe connectors and noticed a substantial and easily perceived improvement. When I added the torque boxes they also added a very noticeable improvement. If you can only have one go with the frame connectors but I see no reason to not have both and the combined benefits.
Torque boxes can easily be fabricated.

70 Dart 340 - torque boxes on 4 speed cars from the factory, same with 68-9 and , and I believe all the big block Darts

I have USCT torque boxes and subframe connectors - they made a great deal of difference in stiffness on a hard launch and going around corners. You don't realize how much flex your car has, until you eliminate it...