Good to know you can get a replacement at ClassicParts. If I recall there were some post a couple years ago and you could not get a new round heater core. I think there are even some post hiding somewhere on this site about fitting a square peg in a round hole because there were few options. .
There actually is one of the Chevy Parts suppliers selling a square heater core that's fitted into a round housing. The mounting holes and tanks tubes line up perfectly with the round ones. I forget what catalog I saw it in.
