Since it's a Benelli USA gun it will not hold the 4th floating shell. It may be a SBE1 but it's the later version that they made right before they came out with the SBE2. The raised rib is also a giveaway that it isn't the SBE1 that holds the 4th floating shell.
Thanks for the info, you have way more Benelli knowledge than me.
Several folks have asked about the ability to shoot light loads. I have shot both federal and Winchester target loads that are 1 1/8 and Winchester longbeards. I have had no issues cycling any of these loads.