According to another forum the difference is
351
Rockshox Pike 351 for Specialized,
95-140mm travel
coil U-Turn
Motion Control damper
disc only
alloy steerer
rebound adj
Maxle 360 included
426
Travel 95-140mm
Travel Adjust U-Turn
Weight* 2435g (5.4 lbs)
Available Spring Tech. Coil U-Turn
Spring Adjust Change Spring
Damping Motion Control
Damping Adjust External rebound,
Lowers Magnesium, Maxle 360 20mm, IS disc mount
Steerer Tube 4130 steel 1 1/8
I have only really ever set up Air Forks so what is the best way to set up the Sag on a coil that from the above spec does not seem to have much adjustment.