You would think that this would be common knowledge by now but so many of us Mopar guys are 20 years or more behind the curve. GM guys have been putting the 200-4R and 700-R4 in classics since the late 80s.
The 518 requires removal of the center section of the torsion bar crossmember. If you plan to retain a torsion bar suspension, you'd need to fabricate a replacement center section with a taller arch in it. Also, there is a few reinforcing ribs in the tail shaft extension housing that can be cut away to obtain clearance. It has been documented at DodgeCharger.com but their search feature is not real helpful. Check their Engine, Transmission and Driveline forum.
Have you done one ?? you have to trim the T bar X member, not cut out the arch & raise it, you just have to thin that area & weld it back.
After that there is a few spots that have to be hammered up for room.
