Stockwellbell

I have a Stoeger M3000 with a 18.5 " barrel. What manufacture and length extension will make the extension and barrel the same length? The model I have is a 31891. I am wanting to have the same look as the freedom series model 31891 FS This. model comes with an extension already installed and a sling bracket on the barrel nut from the manufacturer. I am wanting to have the sling attachment connect at the barrel nut. Not on a bracket connecting the barrel and extension.

Can the Stoeger barrel nut sling be used with any of the magazine extensions manufacturers?