1. Don't know what tab/bracket you are speaking of, on the floor, the firewall or the carb, orig or aftermarket?
Here are some basic stock set ups: It seems like you would want to "start over", Mount one like these below, and use a stock pedal. Your firewall should have the holes already. Attaching rod end to any carb is pretty simple. With a non stock motor, you may have to bend rods to align or use a combination or rod/cable. I can't see your situation from here. There are modifications that can be made to the kits below so as to have a straight shot to carb with rod if carb throttle lever does not line up with bell crank.
http://www.classicpartsusa.com/product/TLK5V8_1956/1956_Truck_Parts_Carburetor_Items
http://www.ecklerstrucks.com/chevy-truck-throttle-linkage-assembly-1955-1959.html

2. No rattles. Floor pan mount may be easier to install. Don't know which one is more stable.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn