Jerry's right about the heater core flow can be in either direction. But it might be better to connect the return hose to the highest port on the heater core to be sure that any air in the core gets purged out and back to the engine. There may be enough flow to flush air in either direction, but it doesn't hurt to help it along. I think Brad Allen has the installation diagram in his photo collection. I'll see if I can track it down.
[on edit] I looked thru Brad's Flikr account, but didn't find the heater install instructions. Too many photos to look thru, and get distracted. If you need something to do (insomnia?) I'd recommend browsing thru his stuff.Should be somewhere in
this album.
