Thanks for that image Rob, which I added here
http://www.picturetrail.com/sfx/album/view/24563589
Send me a PM with your name if you'd like an attribution

The original Diana tubes were inserted into the tapered hole through the breech piece from the rear & are full length

1882 Forest & Stream



Sears 1907 catalog Modified Diana "the barrels are screwed into the breech" from the front



Steel breech with "Washington" tubes