firstly..... you'd need six throttle's not four
it would make gains in a worked form, but in a stock application, it may not be worthwile the expense.
also you would have to change to an aftermarket ecu and run a tps (throttle position sensor) instead of the standard ecu running the MAP sensor.
the only way to get the MAP to work would be to tap into each port and run a vaccume line back to a box so the map sensor can get a reading of the running conditions of the engine.
to make most of six throttles... you'd need, massive ported head, big cam, nice extractors and an aftermarket ecu. basicly a hard tuned n/a set up.