@Scorpion2nz
Congratulations for acquiring this amazing Bing hot air engine. Height is not an issue; you’re very lucky to have stack with it. I would focus on adjusting the cooling fins spacing, and treating the firebox rust by stopping corrosion progression.
My plan. Is chimney and fire box is clean derust and possibly heatproof flat black paint .
Flywheel rim derust and light oil . Rest is just gently clean . Space fins evenly
Cheers
Dennis