Yes when I used a 1″ OD aluminum tube for a frame extender inside frame, there’s just a little bit of slop. I used .005 thick aluminum tape to make a better fit, so the frame ID may be just a tad over an inch. Calipers would be more precise way of checking.
Mike a piece of 1″OD ali tubing is all you need. 12″ if you have a 18″ barrel and 18″ if you have a 24″ barrel. Epoxy a endcap on and fill it with the baffles of your choice. Have you drilled the front bushing and frame? This helps alot in getting rid of a good amount of air.