Joe,

Are you sure the front air bags are the problem? I cannot believe Prevost would use air bags or shocks to limit suspension travel in the full up position. I think your shocks may be too short. Whenever I have replaced air bags I have the body supported and the front axle hangs on its stops, but not on the air bag or shocks.

Have you removed the shocks and measured the distance between the shock mounting points at the extreme down and up positions? Any shock has to be able to compress to the shorter distance (or even a little bit less, and extend to the greater distance plus a little bit more.)