Started the update and seems like everything in the modAPI changed, will take some time to put the update together
Yup. The way that sprites are handled is basically entirely different. There are no more HR sprites - the legacy high-rez are now the default. Probably need to make a new set of fire and light sprites with a higher resolution. I'd recommend hue-chroma shifting the vanilla ones. Should also probably source a larger icon, though I'm not sure how realistic this is.
For the Boiler, sprites are all contained in a pictures (a BoilerPictureSet). You can't access "fire_glow" directly, has to be through that. The "minable" struct doesn't seem to have a "hardness" field in it, but I don't think that matters - it's probably just ignored. "energy_source" doesn't seem to have a light_flicker field at all. Probably ignored. "input_priority" also doesn't seem to exist. Should probably set fire_flicker_enabled and fire_glow_flicker_enabled to true, instead. It seems like that's controlled by power input in native code now - though I'm speculating.
Those are all the differences I could find in the Boiler. Could keep looking if you'd like, but I'd rather not intrude.