Skip the zinc chromate, hexavalent chromate is bad for you- and you don't want to inhale it. And you will be inhaling.

Maybe you can get the non hexavalent kind, now that Europe outlawed hexavalent.

Skip the POR15- it is the same toxic urethane chemistry we badmouth around here

Engine enamel sounds benign enough. But I don't know.

Powder coating shop will sand blast then powder coat?

Not knowing anything about chemical danger sure makes decision making difficult.

Thanks all for the advice,
GFS