heater pipe

By now many of you have already seen my thread about replacing the coolant pipes on my '81 FI car. I've elected to go with the B&W 304SS replacements including the external heater tube. My question is about the internal heater tube that runs in the interior center tunnel from about the...

Wondering if anybody has tried the 1" copper "slide thru" the original in coolant pipes under the car with good results? I've seen it done here on the forum and just wanted some feedback with regards to success rate? Removing the box and fab'ing new stainless pipes at this point isn't even an...