The c-channel frame rails are really not that strong without the cross members. That's why a lot of people box the frame when they do modifications. I swapped in a 390 FE that required removing the trans cross member. I added a deeper cross member below where the original was. Fabbed it from an old c-channel rear bumper. Provided some strength and a place to run the right front brake line. Just didn't feel comfortable not having something there.