Apparently they do fit flow gauges to them some how...but I like your style. That would help in the short term. I do have a lathe and some BSP taps and dies around somewhere.Making an adapter from "integra" fitting to standard 3/8 BSP (flow gauge) would probably work out quite dear?.
Do you have a 3/8 BSP gas inlet fitting on the back of the weldset?, fit the flowgauge there, unconventional but would work.