1100 plugs

[Virginian]

You need to restrict the magazine to 2 rounds for a total of three. That's what these are for.
http://www.ebay.com/itm/Remington-Model ... 43cefc3e52
If authenticity really matters to you, look for some of the old wooden versions.

[Synchronizor]

A plug is about the simplest way to limit magazine capacity in a tube-fed shotgun. If you don't want to order a pre-made plug and wait for delivery, you can make something just as functional out of a piece of wood dowel or plastic rod stock.

[Virginian]

In my younger days, I found a partially sharpened wooden pencil the right length was real easy to drop thru the hole on the Remington magazine spring retainer. With time came a realization that having more rounds available didn't mean as much to me as not having to be ever vigilant to avoid a ticket.

[Synchronizor]

My dad's old Ithaca 37 still has a piece of a tree branch - bark and all - from the '60s or '70s keeping it three-shot legal. I've offered to fit a polymer plug for that gun, but nope, the stick stays.