Here are the GSX "numbers" for Thomas Ruth's A340-600. Just paste it into the (in game) Addons/Couatl-powered products/GSX - Edit aircraft data... (look at the GSX manual if you're confused...)
Everything should work nicely except for the Aft stairs. I spent some time trying to get it to get to the right height but maybe it cannot go any higher. It looks OK, but just isn't perfect. Hope you enjoy it and thanks to Moach who created the GSX file for TR's A330-200, the file that I used as a template to create this.
[aircraft]
nosegear = 27.5
refueling = 1
absoluteheights = 1
[exit1]
pos = -2.4 28.0 4.7 10.0
code = 1
name = main exit
[exit2]
pos = -2.6 10.0 4.75 0.0
code = 4
name = middle exit
[exit3]
remove = 1
[exit4]
pos = -0.1 -27.6 6.5 -7.0
code = 3
name = aft exit
[service1]
pos = 2.5 28.4 4.7 -10.0
code = 0
[service2]
pos = 2.8 10.4 4.9 7.0
code = 0
[cargo1]
pos = 1.6 24.3 2.7 0.0
code = 2
name = fwd cargo door
uldcode = AKE
[cargo2]
pos = 1.4 -23.9 3.3 0.0
code = 2
name = rear cargo door
uldcode = BELT