Sorry it took so long. I drew some things on your picture.
I talked to Frank and in his opinion, April Air makes the finest humidifiers, and he's worked with all of them. You shouldn't have any problem installing it yourself.
I drew 2 boxes on your photo. Box labeled "1", is the best place to install the unit, assuming you have the room. You'll need 6" round ducting to connect it to where you took off your old humidifier. Since the 600 has a side take off, you should only need 1-6" elbow, if installed in this place. Alternately, you could install it in block 2. You'll need a 1/4" waterline.
The April Air is made for 1/4" copper waterline, but you can substitute the plastic waterline used for refrigrators. You'll have to buy the right parts to connect it. Frank said to make sure that you run water through whatever line you choose, to clean it out before connecting.
Also, make sure you change the humidifier pad and oriface YEARLY.
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