http://stevespages.com/pdf/ithaca_3787.pdf is a manual that tells how to disassemble the M37. The picture in step 5 shows the left side of the trigger assembly, including the safety and the plunger. It appears that the plunger could be freed w/o taking the gun apart, as suggested above. If just stuck from hardened lube or corrosion, a drop of Break Free, Kano Kroil, or WD40 to soak on the plunger and on the safety could loosen it. Then, if the safety is still stuck, try to push the end of the plunger in with something that will not scratch the metal.
