There had been talk from some who were reluctant to add a heater core behind the panel because of the perceived risk of burns in the event of a failure in the coolant tubing feeding the core using the typical routing. That concern can be resolved by reversing the orientation of the heater core to have the inlet outlet fittings on the engine side of the firewall.
It can be done, but the only consideration for me was tightening the fittings to the core without damaging the core with no room to put a typical wrench to stabilize the core side fittings. A custom wrench solved that problem. It was fitted onto the heater core mounted fitting on the cockpit side of the firewall as the tubing fittings were tightened. So far so good and heats well.