Well after all that digging, all I found was the literature and a side shot of the A-5
right side receiver.
Here is his write up........
I wanted to mount the Wild West Guns rear sight I had on hand, but it screws into the receiver top. The receiver is too thin on the top center due to the serrations milled in.
There were already three holes drilled in the side for a Williams peep sight, so I found one of those and used it. Natuarally, only two of the three crooked holes lined up with the sight base. It should be fine, but time will tell.
I had the barrel shortened to 19.5" and had a front sight base from a Rem 1100/870 silver soldered on.
Why 19.5"? I don't know.
The mag tube extension is for an 1100/870. They are the same thread, but the M11 has more threads- about 1/4" more. I made a spacer by sandwiching two pieces of angle iron together, and trimming away metal until it also gave me a sling loop slot and a light mount point.
You can take the boy off the farm, but can't take the farm out of the boy. Baling wire and angle iron are wonder materials to me.
I know mag tube extensions are of arguable value, but I like having one so I can load to standard capacity and still be able to shove a slug in.
I got a Browning A5 2-piece carrier from a guy (for the taking) , but I couldn't get it to fit right. It's been a few months, so I don't recall exactly the problem, but I want to say it was a little narrow and would need some shimming to come close to working at all. This makes me think it was for a 20 ga and not a 12. Either that, or a Browning carrier used in a Remington 11 needs some adaptation.