Here's my take on Amelia's mount....
Couldn't find any port tubes with the nice wide flanges, so when rooting around my workshop, I came across a couple of spare Ikea kitchen unit legs. A bit narrow, but nice and strong....
Drilled 4 small holes in the "foot" end, and used No. 6 screws into the MDF base I've fabricated. Tested its strength by giving it a good hard pull - seems solid.
Now, as you can see, the other end has an internal thread, which the height adjustment goes in to (as shown by the one on the right). I've cut the slight flange off the end of the threaded section, and BINGO! I can join the 2 legs together, with a flange at either end. Used some Solvent Weld to fix the threaded section in to one of the legs to it ensures a decent amount of thread in each, and we're sorted. If anyone's interested, I'll stick another pic up when it's complete - currently half painted, so it looks a mess.
The only down side to this bracket is that the tube is too slim to fit a VGA plug down it, so I'm thinking of using some wider tube to cover both the cables and the black legs, that will just sit over them both.
The length of the whole bracket works out at about 25cm - we're going to be sitting a fair way back (15' or so), and the ceiling isn't too high, so I'm happy with the screen to be at that kind of height.