One thing else you should should do is to replace (if needed) the seals on the two movable vents on the heater core enclosure. You will be amazed at how much better the ventilation/defroster system works if you do this. For sealing the box I just used rope caulk from the hardware store, which is also where I got some self stick weatherstripping to replace the vent seals with.

Don't forget the rubber drain outlet on the bottom of the heater box; half the time they seem to be either split or broken off, and then you wonder why your floor keeps getting wet (aside from the leaky windshield seal) when it rains. I just wedge a short piece of heater hose between the bottom of the box and the hole in the transmission tunnel.

Bill