are you sure you have been working on these cars for years
Barracuda-Challenger lesson 101.
It is simple really, both Challenger and Barracuda share the nearly exact same front sub frame structure, but when you have everything bolted on as in exterior panels, the Barracuda becomes a much more ridged car than a Challenger. What the Barracuda has that the Challenger does not is the extra strength by way of a header panel, the Challenger has a full length hood that does not help in any additional strength from side to side.
When you go changing out a crossmember, this case in point is the very robust K-fame that is
THE integral strength of side to side support along with help from a radiator support. The new cross members offered by many do not replace this support in any sufficient way at all, that little piece of box they provide is not enough to help in any way and will allow more flex than you could imagine. They only consentrate on the strength to hold the shock and steering, now way is it enough.