1 should work....most EFI vehicles are set up like that...
I would love to get one of those myself....but don't the O2 sensors only work well around 14.7:1 air/fuel ratio? I think the accuarcy on some gets really poor as they get farther and farther away from 14.7. 14.7 is great for cruising under light throttle....but more like 12:1 is better for power
Oh yeah....i saw a cheap air/fuel guage for $24 at Autozone the other day.......don't think it came with an 02 sensor though....but it is 1/5 the cost of the Edelbrock sensor.