If you're running a 216/235 single mount/double bell housing mount setup using a cross member T5 mount is going to be counter-productive. With the 3 point mounting system the engine/transmission frame flex and stress on the T5 case is not an issue. When you snub the rear T5 mount down, even with adding a dropped cross-member, you're going to be loading up the already limited strength case.
If you're running a V8 with side motor mounts and a single rear transmission mount you'll want to fabricate a dropped crossmember that bolts up under the frame and uses the stock BW/Tremec mount. I have some pics of the cross member in one of my Webshot truck albums.
I base this info on my own experiences with my 235/T5 combo in a 54 AD which has run without a 4th mount (T5) for the past 13K miles. I fabricated a cross-member that could be dropped down when you pulled the transmission but never did tighten down the T5 rear mount. Hope this helps.
