Should be passenger to passenger, driver to driver.
It really doesn't matter though as the heater core is the same on both sides, there is really no proper direction of flow.
"Oil Leak ? What oil Leak ? Oh, Thats Just The Sweat From All The HorsePower!!"
I used 3/4" heater hose and it worked good with no leaks.
"Oil Leak ? What oil Leak ? Oh, Thats Just The Sweat From All The HorsePower!!"