How can the 762 be any shorter than it is now? The existing wing would be too big on a shorten fuselage. I can see a shorten 752 tho...maybe 10-20 feet off the fuselage. The 772 could probably be shorten by 10 feet as well. But I'm not an design/structural engineer so I'll leave it to the experts at Boeing.
As for the A340-400...it did exist, but was quickly dubbed the A340-8000. Named for the 8000 mile range it has. Supposely only a few were built for the rich oil folks in the Middle East. Regards.
"Beer is living proof that God loves us and wants us to be happy." --Ben Franklin