When I bought the air pump for my Road King (the one sold by HG particularly for the air shocks), I casually mentioned the maximum 35lbs (not sure now as to what context). The parts guy looked at me like I was nuts. He said it was very rare to add more than 5-10 lbs of air, 30+ would be ridiculous and was a maximum only, never to be used. When i actually calculated how much pressure I needed, based on two up with light luggage it was 8 or 9 pounds. If you follow the manual, I wouldn't think you could ever get past 12 lbs or so.
I would suggest getting a HD or Progressive (brand) air pump, or similar one made for air shocks. The resevoir is very small, seems like it would be very easy to over-inflate to the extent of doing damage.
Just do the calculations in the manual and try it. If it's too firm you can always let some out. And take care if you do let some air out for you don't want some oil driping down on your rear brake disk.