The Pressure gauge I used was a 1/2" diameter 80 PSI. The standard mounting bracket from the drawings was modified to suit the gauge, There are two options to plumb the gauge to the boiler manifold one being the 5/32" x 40 TPI on the offside of the engine or the top 3/16" x40 TPI port. The option I decided to use was the latter position as this gave more space for the bent copper pipe.
Gauge mounted to bracket
Rear view of pressure gauge and boiler manifold.
Top view
showing mounting position