Thats a hell of a good idea, hot rodders have done much the same for years. Engine block castings however by nature do inhibit "some" rust since thay have a higher carbon content. The better the cast the more carbon, silicon, and graphite are intermingled into the casting. All non oxidizing elements.
I'd think your biggest issue is going to be cavitation or air locking the system.
You going to run a racing style 12 volt pump or standard belt driven system?
You might be able to pressurize or vac. fill the system like on newer cars where the filler has to be remotely mounted do to space restrictions. Your going to have a huge capacity and alot of welds to check out pre fill up!
