Just got the parts today, it is only rough fit but it looks like its going to work well.
Got all parts from McMaster, including the item numbers here:
48935K25 Pressure Relief Valve 1/4" NPT Male, 0-20 PSI
4089K23 1/4" NPT Male Center Back, 0 - 60 PSI Gauge
4429K223 Low-Pressure Brass...