Audi Repair: heater core 97 a6, pressure acid, heater core

Question
Bought this audi from a wholesaler friend, no heat, previous owner mixed fluids producing rust in the system from the phosphates.  friend paid for repair @ dealership.....heater core on receipt but I don't think they did it.......just a pressure acid back flush and a valve tinker. Anyway, am I removing the core from behind the firewall (dash removal) or in front center of firewall engine side? I've already got the dash out. How do I get the heater core out of the centered heater box? My audi 90's were right there as soon as I yanked the dash but this wagon heater core is not as obvious. If it doesn't come out from behind the dash oh well, I just need to know how it comes out of that box.
Thank you

Answer
Once you get to the box, I believe the heater core slides out of the side, but I have to admit I'm not totally familiar with that job; it's a biggie...!  Please let me know how you get on with that, pretty sure it comes out passenger compartment-side, not engine side.