Cool idea to try Heatfire, would take a lot of tweaking and modifying, but in theory will work..... always 10 times harder in practice I'm finding out, but definitely worth a try. At least would be fun making it

Once the boiler is hot and boiling, and fuel is at its highest, the wait is about 1 minute before it steams up to good power (1.5 bar) - enough to climb over stuff, but runs down to less than 1 bar in about 30 seconds, and maintains about .75 bar for the remainder of the fuel. If I wait 4 minutes-ish and not run it, steam builds up to 1.5-2 bars before the safety valve releases the steam. The pressure gauge goes up to 2.5 bars, but it never gets up that far..... unless someone dares to tamper with the safety valve (spring loaded).... ahhh so tempting. Usually it starts leaking steam out of the steam valve or the gauge a bit before it even gets up to 1.5 bars. The fuel tablets lasts 10-15 minutes at a time, but the boiler can hold enough water to have 2, almost 3 refuels of solid fuel tablets.

Keep me posted if you decide on tackling on one.... it sure is a satisfying and fun project There is nothing like old tech, the fire, smells, steam, the sounds....