Re: Heater core, leaking, delete or replace?
"Simplify, then add lightness" -Colin Chapman.
This is the wrong time to apply that. if at all possible, you never get rid of factory defrost. We have run almost as many deluge races in 9.5 years as we have not deluge. We do use the frostfighter grid defroster on one car but it is still not as good...just better than every solution other than factory defrost.
That said, this team already got rid of the fan and ductwork so looping the heater lines is the answer.