This is the newest 12 gauge 8 shot I have assembled from parts I picked up:
Used a later 3" receiver (still slam fire serial 371641XXX MAG) with a set of new Ohio parts for the barrel, mag tube, slide, syn fore arm and butt stock. Had Mahovsky's Metalife hard chrome the receiver and the Ohio parts have their Perma-Coat coating on all of the metal. That's a Trijacon rear sight tapped and screwed to the receiver and the matching front sight glued over the front bead.
Have not shot yet, but it cycles shells just fine.

Sorry about the image

Having trouble

Bumping this and hoping you can post a pic.

How hard is it to install the mag tube? I understand that it’s not as simple as simply threading it in.

Still having issues posting photos on this site.
The mag tube does just thread into the receiver but you have to cut a groove (in the right place) for the little screw that holds the yoke on at the end of the tube. I warmed the receiver (not with a torch!) and clamped the mag tube in a vice w/ multiple layers of cloth around it then turned the tube in as tight as I could just using leverage on the receiver by hand. installed barrel and yoke and marked mag tube for groove. Used 1/8" file and everything worked out fine. Make sure yoke is back far enough from the mag tube nut so you can fully release the barrel.