Lee,
I'm not sure how old this thread is (the recent website changes etc have me more confused than usual) and you might not need another answer to your question but I did an LS3 conversion into a worn out LC2 Turbo Regal and used the factory HVAC system except for the compressor. I do have the heater core valve in place and everything works as it did originally. A/C is cold and the heater is hot.