This may be what you are looking for:
http://marauder.homestead.com/97info.html
Also, to expound on the above post's reference to SASS, the main reason they are not allowed is that Marlin issued a "do not fire" warning on all generations of the 1898 pump shotgun because of a design flaw that may cause the bolt to eject rearward out of the receiver upon firing.
ETA: probably more than you wanted to know about the Marlin:
http://marauder.homestead.com/files/Marlin98s.htm