Remington tactical shotguns with mag extension?

I tried asking Remington, but the response I got seemed unsure. I do not have one to measure, so I would like to ask here. On the tactical models pictured on their site, the magazine extension has a step down near the end. It appears to be like the extension on the military Mk1 870's, but the Remington rep told me that it was not the same.

All I need to know is, will an M7/M9 or similar bayonet fit over the step down?

Thanks!