While that is a good idea there would be to much movment on that sling plate. And if we madeit tight enought where there was no movment you would not be able to take of the mag tube.
That said we just paid for and exstrusiton die, to make a 2pc mag tube clamp which can have a short bit of M1913 rail attached to it.
But that may not be ready for a few months yet
But it will be 1/2 the price of. May clamps on the market
You would know better. Here's the ggg one for the m4. http://www.gggaz.com/benelli-m4-slin...mbo-mount.html Maybe get the wheels turning.
Where you thinking something like this.http://ecx.images-amazon.com/images/...UL._SX300_.jpg
And have it clamp onto your extended tube. That would be great