The 6" center drum is ASTM-A106 Schedule 80 tube. The coils are wound from good quality 1/4" Schedule 40 pipe (A53 I think). According to the piping charts they both have a working pressure of around 2100 psi. It will be ran in the 400 psi range. I doubt the 1901 Loco engine would like 2100 psi
Should do a pretty good job, my buddy has a similar boiler with only 12 coils and it runs his 2.5 X 3.5 twin Mason very well.
The fuel tank will be schedule 40 6" pipe with endcaps inset. It will have an air over fuel pressure in the range of 80 psi.
Going to use kerosene as primary fuel, or gasoline/petrol as a backup. These will burn about anything. The burner is a vaporizer tube type. The burner itself will be an Ofeldt style. The burner is similar to the boiler, having a center drum of the same diameter and tubes that go out radially in a sunburst design. These burners do not emit flames under the center drum of the boiler. We have surmised that doing so would disrupt the internal circulation of the boiler. Whereas flames impinged on the generator tubes pull water in from the bottom and emit steam at the top back in to the center drum. Any water simply goes back to the bottom and then re-enters the tubes.
These are very powerful generators for their size. Similar to a flash boiler, but the center drum provides some reserve.
I'll post a pic of the chassis in the "Anoraks corner" section.