Hard anodize it so the threads won't get worn out. Powder doesn't sound like a great idea... you'll have to mask off all the holes, and like paint, it can chip off. You wouldn't want any of that stuff inside your carb.
Reputable coaters use these cool things called High Temp Silicone Plugs that keep powder out of threaded holes. Chipping is rare if the job is done right (it is typically attributed to under- or over-curing, oils or other contaminants left on the substrate under the powder, or using a powder with a low tensile resistance on an improper application).
Anodizing fades over time and scratches easily ... as we all know from our factory trim parts.
