e.alleg, Congratulations!! That is a real find. That boiler is still just a 'teenager'! Do you have force air heat or hot water heat in your house?
Ebay often has some pretty good deals on heat exchangers, both water/air and water/water. Search Ebay under 'outdoor wood boiler'. If you don't find what you want I may have some links to other companies.
Dungeon Master, that was a steal ! You will really enjoy using that Mark III. It will even burn that 'reclaimed' butuminous you bring home.