Not sure if I would use Panel Bond on an area for chassis stiffening on an old car not designed to use it.
Panel Bond works best if there is a large area of overlap, and the two surfaces have to be parallel and flat to each other, so when the panels get clamped together and most of the Panel Bond squeezes out. If you leave it too thick, those areas just pop apart and the Panel Bond just peals away. Then it just rusts away where if pealed apart... And from my experience if its used in a place that will fatigue, the panels pop apart.
Just weld your chassis stiffening on. Most people complain about overhead welding because they don't suit up and protect themselves from sparks well enough. And most people are over trimming their US Car Tool subframe connectors because they aren't forcing them into the floor pan with a jack or pushing their sheet metal floor down to weld them.
I'm definitely not sure what value a glued together classic car is going to have.
