Air assisted forks or go with progressive springs

My 81 GPz 550 has the air assisted forks, when I bought the bike there was no air in them. Tried to pump them up with a tire pump but couldn't get the hose fit on the air valve. As I just purchased the bike, I don't know if they will hold air. I've read here that you can delete the air assist by replacing the springs with one's from progressive suspension and changing the caps.

First off, what models didn't have this option so I can find caps that will fit my bike. Can I change the springs myself? I have had extensive automotive experience but no bike experience. From the Clymer manual it says to depress the top of the fork and removed the circlip. Are these regular circlips with holes at the ends so you can use a tool?

With the progressive springs, on their website under the "fork springs" they state: "You must add a spacer (length indicated) to spacer furnished with springs or make a spacer that is the same length as the two combined." The number of the spacer is 19. What does all this mean?