Don't put a 50 psi full scale pressure gauge on a regulator that can give you 200 psi output. It is highly likely that you will one day ruin that gauge if you do. I would leave the gauges on the regulator as they are, and just install the needle valve, solenoid valve, bubble counter on it. Two stage regulators are intended for uses where the outlet pressure is important, so they will have good output pressure gauges already installed. (If the regulator was made to be used with remote gauges it won't have gauges installed, but most of them do have them. The ones made for remote gauges will generally be the best quality though, since they will probably be made for laboratory uses.) Just try to get one where the regulator max output pressure is only 100 psi or so, so it is easy to read the pressure when it is around 10 psi.