I too am in the process of stripping my engine bay, I found that heavy duty Aircraft Coating Remover did a great job, not sure about the effect on any zinc coating. Is the zinc coating necessary to have? I'm not a paint pro, just learning as I go... is it possible that it was just an etching, rather than zinc? Unless he had the car dipped, in which case I could see you not wanting to ruin that.
I found that when I used the stripper, the metal underneath appeared to have a dull grey finish (this was under factory paint). I'm guessing yours wasn't at all like that.
In any case, stripping the bay seems to be a complete P.I.T.A. operation, tons of time and patience and the right wire brush attachments seem to do the trick on my application. I wonder though, for yours, if you won't have to etch the metal once you remove the paint? Does a zinc coating accept primer normally?
I'm interested to see if others know the answer to this.