Swimjim was asking for a way to test the Intermediate Pressure on his Dacor Double Hose regulator, so I threw this together one afternoon. It's pretty crude compared to the fine tools that Herman makes, but I figured it is a start... and it works.
Here is the basic adapter installed in place of the second stage body. It slips right in and is held in place by two screws, just like the 2nd stage. The retaining washer is slotted to accommodate a reg with fixed flow vane, but you can just turn a variable vane to the side.
Here is a look at the basic components:
You can attach any components you wish into the 3/8" x 24 threads, which is the standard low pressure Scuba port size. Here is a little rig that incorporates Swimjim's idea of a tee with an outlet for a scavenged demand valve from a single hose reg 2nd stage. That serves as a relief valve and a bleed valve that you can manually drain the pressure with. There is a quick disconnect for your IP gauge.
Also, in the far top port of the tee you can see a pressure relief valve like those used on early tilt valve (upstream) second stages. Not needed here due to the second stage valve also being installed, but just to show another way of protecting your gauge, hose, etc. They are still available through Trident.
I think VDH can order those for you.
Here is the whole works in place and ready to use: