Karlos, you can use the fuel computer on the EFI version, you just do not connect one of the earths and wire strraight to the ECU outputs.

Pins:
1 = red = Perm +12V
2 = grey/green = Lights +12V
3 = brown/red = Fuel remaining on sender
4 = not used
5 = brown = Earth
6 = brown/white = Speed sensor
7 = brown/green = Fuel flow (pin 17 on ecu)
8 = not used
9 = black/yellow = Ign +12V

If you leave the other earth connected, you will not get over 11mpg max as the calculations will be incorrect.