BB.
No clue if this helps--and a little out of my skill set--but a quick consensus at Club Octane points to your S/N having a max cruise of 121 knots per the FAA TCDS (2A13). It does show a reduced maneuvering speed though:
XV - A.- Model PA-28-181 (Archer II), 4 PCLM (Normal Category), 2 PCLM (Utility Category), 8, 1975, for S/N 28-7690001 through 28-8690056; 28-8690061; 28-8690062; and 2890001 through 2890205.
Airspeed Limits Never exceed 171 mph (148 knots) CAS
Maximum structural cruising 140 mph (121 knots) CAS
For S/N 28-7690001 thru 28-7690467:
Maneuvering 124 mph (108 knots) CAS
For S/N 28-7790001 thru 28-7990589, 28-8090001 through 28-8690056, 28-8690061, 28-8690062, and 2890001 through 2890205:
Maneuvering @ 2550 lbs. 128 mph (111 knots) CAS
Maneuvering @ 1634 lbs. 102 mph ( 89 knots) CAS
Flaps Extended 115 mph (100 knots) CAS
And as NL mentioned wheels pants can be removed, but I'm not sure if that note (24) is applicable to your aircraft.
But as you pointed out:
Piper Seneca & Cherokee Cruise Modifications - Laminar Flow
Piper Main Gear Fairing Set (STC'd) (60-MGF-18D) - BuyPlaneParts.com is the Texas Aeroplastics online store
Piper PA-28 Wheel Pants and Fairings by Knots 2U.
I might be totally wrong on this, but good luck.
How did your corrosion issue work out?
W1