I have one of the Facet solid state metal "box" type units mounted on the inside of the frame near the front of the engine. I believe they recommended that it be mounted on a slant (but it's been A LONG time - best to check for their recommendation). As long as it is solidly mounted near or below the level of the bottom of the fuel tanks, I don't think it makes any difference where you mount it.
BDA is right about needing to mount the electric fuel pump as low possible. Don't do what I did and mount the pump on the engine bay fiberglass above the frame rail. The picture is from my S2 but should be applicable to the TC. After letting car sit for a week or so and the tank level at well below half tank, the pump tick forever after turning on the power and never fill the carb. I'm assuming that the suction lost prime and the pump had insufficient suction head to suck the fuel from the tank. Adding a couple of gallons usually fixed the pump issue. Moving the pump to a lower level apparently solved that problem for good.
I seem to recall a discussion on the Yahoo list a few years ago that powering the electric fuel pump directly off ignition power may cause electrical spikes affecting the tach signal. Might be worth while investing in a relay for that purpose.
When the fuel tank level was less than half full