PATC has a kit that can control the overdrive and lockup, but nobody makes a transmission cross member or replacement tunnel that I know of. Most of the conversion articles I have read just make up a cross member from the ends of the original crossmember and dropped center section with a new transmission mount. PATC has a article on the conversion here:
Dodge 727 Transmission Swap to 518 Transmission from PATC, 46RE 47RE 48RE
Original PATC conversion kit video:
Modified with different overdrive switching point and time delay for lock up:
With adjustable pressure and/or vacuum switches, you can change the overdrive and lockup points to suit your requirements. The person in the video was running a 3.91 rear end gear. If you run a lower gear (2.94, 3.23 or 3.55) the PATC standard shift options may work better. The guy in the video made his overdrive shift point at 40 MPH to save gas. I could see where a street driven car with lower gears might be better off shifting into overdrive at a higher MPH, based on a standard to mildly modified engine. All depends on what kind of driving you do, the power band of the engine, and what kind of a highway/city street driving split is involved.