GunGeek,
Didn't notice that you mentioned yours was plastic in your post. The one in the pic and the one I have are both the original Remington made version which is metal. You have one of the recently made versions that copies the original Rem version.
Don't know about using the sidesaddle with the plastic version, probably now way to make it work.
About the only way to get the Remington metal version is to find one used for sale. I know there was a guy selling a bunch of them on E-bay awhile back that he had refinished. I picked mine up used many years ago