My experience was similar to BlackR32. Plenum off, and of course replace ALL the coolant hoses while you're there so you dont have to take the plenum off again, which is a bitch of a job.
Here's the part numbers of the stuff i replaced, and IIRC I missed the two elbows going to the assembly that holds the AAC.
21307-05U02, 14055-05U11, 21307-05U04, 14055-05U01, 14055-05U02
Water/heater: 92410-05U00, 92402-05U00, 92401-05U00