The reason Toyota changed from external to internal pumps was an engineering improvement. It required less amps to push fuel through a 5/16" line for about 3 extra feet than to suck the same amount of fuel through a 1/2" hose the same 3 feet. Its also less wear and tear on the pump. As I also discovered quite unfortunately, at higher altitudes, the external pump setup tends to more readily cavitate, meaning the boiling point of the liquid decreases on the negative pressure side of the pump such that sucking air bubbles through the impeller causes the pump to burn out. Gee, where do you get a replacement high-performance fuel pump on top of a mountain, let alone a warranty replacement, hmmmmm???? Having to do it over again, AND I will eventually, I'd stick with the internal pump and go with a Walbro or similar.
If you've got a stock external pump and want to upgrade, then you'll need to be ready to fork over some serious dough for a Bosche VW or Porshe unit - what I'm currently running.