I want to replace the anode tube on my AO Smith GPSH Powershot gas water heater. Problem is, I can't find it. From the parts list diagram, it appears to be accessed from the top-front. But the blower housing is covering it. So my questions are:

What should I remove to access the anode rod?

If I need to remove the blower housing, what's the best way?
In removing the blower housing, does the rubber sleeve (for the 3"pvc exhaust) loosen and slide up or down?

AOSmith's website shows the current replacement for 183523-29
to be 9000029005 which I believe is a magnesium anode rod.
Other sites show replacement as 9003944005 which is aluminum. Any suggestions on which one to choose. FWIW, we're on city water with low iron and 20 hardness.