Like I said, I didn't know if those things are now being produced or not - I just know they weren't when I needed them.
The rear shock cross member is one of those items that stops with the '69-'70 unit. On Q's advice, I bought a '69-'70 repop unit and sectioned in the shock pockets to repair the originals damaged by irresponsible use of air shocks. I believe the repop '69-'70 units are slightly narrower than the '71-'73s, but are otherwise similar in design. The repop unit materials were MUCH thicker and stronger than what was replaced on the car (3-4x thicker metal, actually) - I could probably run air shocks without any fear of damage now... but I'm still ain't gonna.
My car has standard (non-staggered) shocks, which is why I mentioned it.
The E-brake cable I mentioned is located underneath the car, in the area inboard of where the driver side frame rail extension and upper transmission bracket meet (directly across from the e-brake cable idler mount, which is also welded to the floor). After passing through the floor, the cable feeds through holes in the rail extension, and fits through a keyed hole into this bracket with a giant Bobby-pin-looking clip to hold it in place. I had to fabricate that one 3 times before I got it right - mine literally disintegrated when I disassembled the floor pans/frame rail extensions to replace the floor pans.
I'm sure you're right on the other items you mentioned are now being made (kick panel sheet metal, etc.). I wasn't aware of the front tank mounting bracket, though. I got some sheet metal and was thinking of bending my own replacement, but then asked Don from OMS about it - and he actually had a few good ones from some of his parts cars... and that's where mine came from.