The first step is to get your hands on the proper heater core. I purchased the heater core at Checker Auto for $25.00, although Auto Zone, Pep Boys, or any auto supply should have the 1976-1986 Chevy Chevette heater core. The stock hose barbs were removed and replaced with brass 1/2” barbs. You can also use 3/8”. I cut the stock barbs off using a small tubing cutter. Cut off the barbs as close to the tanks as you can.
The Chevy Chevette heatercore
The next step was to shape the brass barbs to fit inside the copper tubing. The left side of the tank is 5/8” copper and the right side is 3/4” copper tubing. I purchased two brass barbs, one 1/2”x 3/8” thread and the other is 1/2”x 1/2” thread. I first placed the barb end into the chuck on my drill press. I set the RPM at 2500 and then used a coarse metal file to shave off the threads until each barb would slide into each copper tubing on the heater core. You'll then need to apply some flux and then solder each barb. I used a propane torch for this step. The solder used was Silvabrite, which contains 95.6 % tin, 4 % copper, and 0.4 % silver. The flux is Copper Mate brand. Just do not apply to much heat near the tank as you do not want break loose any solder holding the old copper barbs.
Filing the barb