Pritchard had one of the best-thought-out steam systems in the era when 'pollution control' was the thing of importance, and mileage in 'comparable' gasoline vehicles often abysmal. The layout still remains a good one, with the condenser and air heater up forward where cooling is enhanced with speed, the engine in the front, and a transmission easily used to keep the water rate in line with combined speed and load.

I don't recommend using any kind of tapered monotube or 'once-through' arrangement of the Doble and Besler kind unless you love to tinker in the shop, on weekends, and by the side of the road. Use the small LaMont that the SACA 'phorum' discussed extensively a few years ago. This uses forced circulation (about 6x peak steam demand) in what is basically a waterwall firebox designed for good flow; the water is run through a cyclone at saturation pressure (the water spiraling down and the steam separation being done with minimal splash even if using Porta treatment) and a practical 'hotwell' being provided also at saturation pressure for recirculation. Steam is taken off an elevated 'dome' above the cyclone, on the principle of those tall domes on rotary-plow engines, and is then superheated in the normal way in a 'convection section' like that of an industrial HRSG (completely full of tubes, with the header entirely above the shell for proper steam separation there. Superheat can also be arranged 'separately fired' like the arrangement on the enginion AG/"ZEE" ultrasupercritical motor -- using modified space-shuttle tile sputtered with catalytic material for distributed self-ignition.

A major point of the LaMont arrangement is that no special BFP is required on the high-volume circulation, as it is entirely at saturation pressure with only a few psi of head involved. This means that the parasitic loss for the circulation pumps can be very small, probably easy to supply and control electrically.

You can provide a reflex pass through a Franco-Crosti arrangement to extract energy for the Rankine cycle from the combustion plume down to the condensation point of the combustion water. Since the likely fuel used for this would be ULSD biodiesel, the historical complaints about dew point of sulfuric acid and SO3 no longer concern us. If you provide two-stage condensing (one with leaky tubes to facilitate Holcroft-Anderson recompression of the exhaust steam) you can fine-tune the percentage that gets 'evaporated' down to the critical saturation temperature for the recompression to work correctly at a given mass flow, and this may prove better than the time-honored method of 'misting' the condenser with relatively untreated water (as on the second British 'Electro-Turbo-Loco') to keep the condenser effectively unchoked even in severe operating conditions...

Mackwell Locomotive in New Zealand is developing a Lamont boiler for steam tractors and small steam locomotives, for use in developing countries. https://mackwelloco.com/locomotive-boilers/

Interesting drawing - there's in particular a big red thing in the middle marked "advanced combustion system" that i think needs some clarification.

Full brochure here:

https://mackwelloco.com/locomotive-boilers/

Note the very thick, inclined coal bed with the three little mystery blue arrows coming up from an undefined somewhere as the primary air. That indicates to me, in conjunction with the 'zero char and cinder throwing' that this is GPCS firing, which jibes with the 'advanced combustion system' chamber required for better radiant uptake from transparent as opposed to luninous combustion plume away from the grate.

They show a very short centrifugal steam separator, mounted 'down' rather than 'up' as my designs would have it. The separated steam goes nearly immediately into what looks like a monotube superheater coil -- this has been done, in my opinion, to preserve the 'heritage look' of the replacement boiler as a whole -- in typical LaMonts, the steam separators are considerably tall, with the 'steam dome' equivalent being at comparable level above the cyclone entrance port(s) as you'd see in a conventional firetube bpiler above the peak 'swell' that might form under the dome and dry[pipe mouth. Note that there is no place to put a secondary system like an Elesco 'steam dryer' or active centrifugal element in the small space before the superheater element. This might entail very, very careful throttle control (perhaps necessitating an air servo or interposed dashpot in a mechanical throttle linkage).

Extra kudos for mentioning Shaun MacMahon's "Porta Treatment" which is optimal for this system ASIDE from increased dependence on antifoams that may limit the effective peak pressure and saturation temperature ... this being an often carefully-unvoiced concern about the 'consumable' part of PT as it was classically developed. On a 'heritage replacement' it may be relatively easy to trade water for steam a la Tuplin and run the boiler at larger mass flow of lower pressure, making up for the increased mass flow with a higher degree of practical superheat.

In a real potboiler of a movie which I saw as a kid, "Guns of the Deep South" Civil War cannons are double-shotted and wrapped with piano wire to hold them together when they are fired from a mountain top.

https://www.imdb.com/title/tt0043482/?ref_=tt_urv

Many comments have been posted on different forums about what a bunch of baloney this was. Hey. It's a movie based on a fiction story.