Good point. The GSL393 (lower volume) is what RWS (Tracy) was selling before he retired.
FWIW, I toyed with the idea of using electronic pump control (PWM) to eliminate the need for a mechanical regulator. I called Walbro's tech line & he said that we shouldn't use PWM (which is fine on turbine style pumps) with gerotor pumps because the constant square wave pulsed supply voltage 'hammers' on the gears in the pump & greatly reduces life. But he went on to say that it's perfectly ok to run the pump at lower voltage to reduce the flow. So it's possible to insert an adjustable DC power supply in the supply to lower its output. Not necessarily recommending this, since it might introduce other 'issues' (reliability being one), but there you go....
Charlie