I don't know if this will help you with the SBEII, but below are links to a picture I took this morning of the underside of two of my M1S90 bolts. Maybe the SBEII bolts are similar enough that you'll know where to look for the extra cut.
BenelliBolts (small JPG, 60KB, less detail, quicker download)
BenelliBolts (large JPG, 564KB; same picture, more detail, but longer download)
The newer bolt in the pics is on the left, with the finger-curved bolt handle. This came from a newer M1 Tactical, and will NOT do the extra shell on the carrier.
The older bolt is on the right, and will do the extra shell on the carrier. It came from an older HK-marked M1 Field.
The only difference between the two bolts is the extra horizontal cut on the lower-right side of the bolt. (Use the dime in the pic as a reference: FDR is eyeballing the extra cut.)
Each bolt works in either of my M1S90 shotguns. The extra shell capability follows the bolt without the additional cut across the bottom.
Looks like a little J-B Weld to fill in the cut, or some careful welding/brazing, followed by a little time precision grinding the fill area smooth and level with the rest of the bottom of the bolt, should get you Benelli owners with the newer-style bolt that extra shell capacity you're looking for.
[ 02-08-2005, 11:00 PM: Message edited by: Schiessuebung ]