But it's still possible to run lean if the maf calibration isn't just right, he might hit a certain maf hz where it could lean it out. But I doubt you'll gain more than 1 psi with the small pulley drop.
If his afr is good now, dropping .1" on the pulley size isn't going to change anything.
2001 GTP Drag Car - XPZ, Tischler heads, Upsidedown M90 IC'd, e85, Gen V, 2.3 w/ 5%OD
2005 F350 6.0 - studded, deleted, tuned
2001 GTP - cam, headers, nitrous, stock trans - 11.83 @ 116 <$2k in mods - sold