The problem with the Greener Cross-bolt is that when a gun is tightened (and a good many vintage Brit and European guns which worked for a living have been, at least once in their life) the cross-bolt must be tightened too. Often this step is neglected (too hard) and the gun (which may have depended on a contribution from the crossbolt by design to remain tight) will then shoot loose relatively quickly.

That photo of the Manton-retailed Suhl .405 double is from Century Arms, however my good friend Rob B_ has one and I will attempt to post some additional photos of it soon. If I recall, the only camera available when he last had the rifle in Darwin was a really crappy digital, so they won't be brilliant! That gun is also illustrated in the Manton catalogue of the period, I could scan the relevant page and toss that up too if you're interested, banzaibird.