I was very blind lucky and stumbled onto a pretty good condition Norton Atlas gear box. I was looking for a BSA pre-unit A10. But the Norton came my way and in, I hope a bit of karma, it was good. The Norton box is smaller and has two very substantianol mounting lugs. Plus, I noticed it has a decidedly egg shape to it that will allow it to nestle right up against the engine case and help control the center of gravity. And of course with the gear box and engine being coupled it should contirbute to the rigidity and overall strength of the main triangle of the frame without adding lots of extra steel. I have also noticed, from peeking at other builds, that the Norton can be rotated around quite a few degrees before you start having trouble with kicker and shifter fouling problems. I'm not contemplating anything radical but it's nice to have scored a box that has that proven flexibility in mounting choices.
I will be looking for a replacement clutch adjust cover plate which has Norton scribed on it. I have seen a few but never run across one yet. But I haven't really looked hard either. I don't want to hide the provenance of the bits I use.
And after all, if the Norton Atlas box is good enough for Big Sid and Matt Biberman to use on their Vincent Comet build, Overtime Tina, well it should work fine for my Overland.