I recently had subframes welded into my '63 and the difference was very noticeable.

We made sure and did it with the wheels all bearing the weight of the car.

The guy that did mine did it a little differently as I didn't want to interfere with the floorpans. He cut the front of the rear framerail out to where the 2x2 steel slid into it. The 2x3 that most people use is overkill for anything but a full on racecar IMO.