UPDATE - Reassembled everything this morning. Filled the resevoir with antifreeze. Fired it up and watched as all the antifreeze drained out the exhaust
Found a rad pressure tester and tried to build pressure but could hear the air escaping within the resevoir / heat exchanger housing. Pulled the entire housing off and with the help of a couple of people we we able to plug
all the outlets and pressure test again and there it was. Some small holes had corroded through low on the resevoir at the exhaust mainfold just before the exhaust elbow. Note to self: next time take the entire resevoir/heat exchanger unit to be tested not just the tube bundle. Its just six more bolts and 2 more hoses to undo.
should be painted gold not green ...$1000 for a new resevoir housing
Are we having fun yet?