I wouldnt think it would matter what size nozzle you are using to be able to utilize a metering pump. The idea is that you can get rid of your constant level tank because the metering pump will deliver the same pressure regardless of your supply tank pressure.
Most burner pumps, from what I understand, have a valve in them that only allows them to pump when they reach a certain RPM. This isnt suitable for a metering pump. You want a pump without that valve so you can turn it at a low RPM and deliver the precise amount of fuel needed for your siphon nozzle.
As for the regulator, I wondered that myself. Maybe a solenoid valve should be added before the pump to prevent any flow when the pump is off? Maybe some with more familiarization in metering pumps can help us out there.