2X2 fits perfectly under the floor on 69 B-body. Just cut a hole in the front of the rear frame rail, slide the 2X2 inside the rail and then up against the back of the torsionbar crossmember. Without a doubt the easiest weld in frame connectors ever.

Not so good on an E-body.

In theory, there is no difference between theory and practice. In practice, there is.