I have done it. It is tedious. The area around the OE pedestals is jacketed......meaning, there is water under there! You have to be careful not to go too deep, and only as far back toward the spring seats as is absolutely necessary. A ball nosed end mill, and a chamfer on the T&D subplate are a good idea. I have also milled .050 off the subplate to aid in avoiding breaking into water. That requires shortening the eight 7/16 fasteners so they don't bottom out. It is doable, and you can weld up a boo boo if you break through, but you just have to be careful not to open up a problem there along the back edge of the subplate. As far as offsets, the Medium Riser set-up will work, on-center. There are a few shims that can be moved to take care if the side to side locations. The problem is that the pushrod will always be located further up toward the valve cover rail with the pair shaft T&D. The original tube has to come out, and a new elongated tube has to go in, in the right place. Much more work on the manifold than the head to make all that stuff work on a Tunnel Port.
