My thought was to use the T-fitting on top of the steam line for your pressure gauge, so you could put your original Jensen safety valve back in place on the boiler.
The pressure guage is a #12-32 for banjo screw. The hole is a 12-32 female. I’m not sure there are any fittings for that.
It was designed to go on top of the steam line coming from the banjo screw, thus why I have a teflon bushing there.