Single plain intakes for small engine with FI

OE applications are not really single planes or dual plane. The runners are so long they act like a dual plane.
This does not matter if you are talking about modern throttle body injection like the Fitech. Throttle bodies still mix air and fuel in the plenum, so the intake has to work well with the mixture.
On full actual fuel injection, not the throttle body stuff everybody calls fuel injection, you are only flowing air, so those really long runners can be used without risk fuel puddling anywhere.
If you want to run a throttle body injection system, most guys find it works better at lower RPM if the plenum is not fully divided. So a single plane is fine, and dual plane is fine if the divider has an old school notch in it.
I should also say that a Fitech system is not going to increase your horsepower much. Maybe little from better fuel atomization, but no real increase. Just easier starting.