Ryan,
My computer is in the firewall under the brake booster. The '93 location (in both Explorers and Rangers) is the passenger kickpanel. My truck was one of the last '93 models built - Ford had already started with the '94 mounting location.
The drawback to the firewall location is to get the computer out of the truck, you have to loosen the inner fender. Not hard, just a pain in the butt.
Wiring is easier with the ECU under the hood - all the wires do not need to pass through the firewall. But, the computer is subject to water issues.