As I mentioned earlier, the factory Datsun transmission mounts had to be completely removed to clear the VQ 6-speed transmission. I wanted the transmission cross member to incorporate the factory VQ transmission mount and have room for a dual 3" exhaust.
Transmission clearance is very tight in the 240z tunnel, and this dictated the final position. With ~0.25" clearance at the top of the transmission the bottom sat flush with my sub-frame connectors. I did a rough check of the drive-shaft alignment using lasers and it was reasonable.
I used 0.188" plate for the ends and then provided clearance for the exhaust using the same 4" round tubing from the engine mounts. I tied the center together with 0.125" plate. After everything was fitted and welded, I added a couple gussets to the sharp joint where the tubing met the outside plates.
MIG welding it made the job go a little quicker and it looked great after a little cleanup and powder coating. The powdercoating was done in house using an Eastwood Hobby gun and household oven. I've been pretty impressed with that equipment for the money!
To finish the installation I added some additional reinforcement to the floor pans where it bolted through. the reinforcement spans between my 2x3" sub-frame connectors and travels up the tunnel a bit to tie everything together. I welded nuts in place to make R&R easier when the interior was back in place.