Are the 3" manifolds you're talking about called "I Beams"? I have a pair and it looked like the exhaust pipe clamps to the manifold - these came from a 351 from a larger truck - I used a pair of 351E manifolds and yes - they constrict the exhaust down to the same lead pipe that the non-magnums use. Figured I would use the big I beams when the time comes to replace the pipes from the manifold to the "H pipe" I use.
