Hello: Nice 😎 It’s good to see old stuff brought back to life. Comments from the peanut gallery. As you’re going to be heating relatively cool water, there is a good chance you’ll get condensation running off the copper coils down onto the cast iron floor of the heater. You might want to coat that with something that will take high temperature, to slow rusting. Also, should you ever get a leak in the coil, don’t worry; just get out the Mapp gas and 5% silver solder and fix it. No problem. Lastly, don’t valve things so the heater can be sealed off. Somebody could close the valves, fire up the heater and have an explosive mess on his hands pretty fast 😯 Hope you’ll post a picture!
ps. I’m not sure I know what you mean by “electrolytic rust removal”. Could you explain?