I just finished installing new axle, wheels and Samurai springs under my M101 yesterday. It has a lid, RTT and box full of gear. The weight is about 1,200 lbs (need to get it weighed) and the springs appear to flex well with me pushing and pulling on the trailer. Springs settled down to a point that gives about an inch of lift over where the stock springs were (23" at hitch), so my Napa shocks are still good to go. Plan to do some offroad bump/washboard testing this weekend to help determine if the optional extra spring leaf is necessary. May go the optional spring leaf just for comparison.
FYI, Jay gave the eye measurements for springs above, but on the Samurai the shackles are forward near bumper, this is the reverse on a trailer. So the bigger eye would be front, smaller rear.
BX