Heater Tube Repair/Repop

[Calif240]

I've got a '69 that I'm restoring the AC/Heater Box on. The copper tubes that connect the heater box to the firewall were partially corroded and stuck to the heater core. I had to cut part of the heater core tube to get the two apart (the heater core was busted anyway, so I bought a brand new one from Classic Auto Air). I've tried everything I know to get the piece separated (heat + vice grips on the end, penetrating fluid, etc). Anyway, can anyone offer another suggestion to get the parts separated, or lead me to someplace that might have these repopulated? Any other options? Is it possible to just build new ones with copper piping that is connected to a flange? Any advice would be great...

Thanks,

[PlainfieldCharger]

Sounds crazy...I would try lemon juice over night....