Sorry, I just saw your PM today and responded as follows:
So, both of the heater hoses should be clamped on the engine side of the firewall per GM design. If one of yours is clamped on the inside that will necessitate the removal of the engine side heater box. This task is easier said than done however because 1-2 attaching nuts are well inside the cavity between the fender and fender liner. It's usually best to drop the fender liner to access them, but with long arms, a flexible light and a mirror it can be done without dropping the liner.