MSH out of the pistol, Cock the hammer back, then move the thumb safety to about the middle position and work the thumb safety out of the frame/ past the detent.
With the both safeties now out of the pistol, load the leaf spring, then slip the MSN-Mag well up enough in the frame to hold the spring in place (but not enough to allow the MSH plunger to touch the hammer strut with the hammer cocked). Now slip the grip safety back in, and load the thumb safety back in the frame (again remember that the hammer has to be cocked to allow the thumb safety to go back in). Lower the hammer, and then make sure that the hammer strut is loaded center of the plunger as you fully raise the MSH-well into place.
P.S. Next time you go to pull the MSH-mag well, tape the grip safety all the way in. It will retain the leaf spring in place and prevent the sear leaf from springing out of place.