According to this chart, it's 58 psi.

http://www.peachparts.com/shopforum/showthread.php?t=23833&highlight=722.351

If you need to replace your modulator, ask for part# 126.270.91.79 at the dealership. It's an updated modulator kit that comes with a new style thrust pin, miniature t-wrench, cap, and o-ring. Installing and setting modulation pressure for the updated modulator is done in exactly the same fashion as the older version.

The reason for the update is unknown, but I feel it's mostly for convenience. The cap, which is now plastic, features a handle for 'fine tuning' after you've set your base modulating pressure. Turning the handle counter-clockwise will subtract up to 3 psi from your base pressure so there's no longer any need to pry off the cap each time when adjusting by shift feel.