Benelli M3 can use SuperNova Collapsible Stock. Replace dummy tube with adjustment rod.(with modification to 166s adjustment tube)(Not all M3's need the 166s Adjusment tube rethread Some M3's fit fine)
Yes it Will fit all you need is the SuperNova Collapsible Stock and a Supernova or MR1 Adjustment Rod.
(for modification use this link below)
http://www.benelliusa.com/forum/showthread.php/31455-benelli-m3-super-90-with-super-nova-tactical-collapsible-sock