How big is the engine.
Blackgates amongst others do a small vertical boiler kits suitable for a stationary engine.
They also do flanged plates for LO86 which has to be a Myhobbystore plan no.
My experience is not great on this – I have run in a traction engine and a Metre Maid on air. They go much better on steam, well the TE does. The MMs two engines are still running in, which means constant oiling while running, and cleaning up as water in the air condenses and covers all the internals.
What to run it on. Coal if youll put up with the inconvenience, gas would be cleaner and easier. Depends on the size too.