Hi Oscar welcome aboard
Another Student of Mr Zaks eh!! Me too and Lance leventhal, but remember Their work is z80 based not zx81 and as the little door wedge is wired in a very non standard way not all examples work.
A few other useful sites..........
http://www.retrocomputermuseum.co.uk/forum/
A forum member called Womble Is from Your part of the World (Yes I Know Oz is bloody massive)
The German ZX81 forum.........
http://forum.tlienhard.com/phpBB3/viewforum.php?f=2
Google translate v useful here
And for trading..........
http://www.sellmyretro.com/
Rich Mellor who runs the site I find to be a good honest trader ( crap I owe Him some feedback!)
Read all the threads Oscar, some good stuff going on, and if Your house lights go dim It's just Lord morris ( should be Sir Morris But I'm in His debt) or Andy Rea switching in another generator to run their latest projects!
regards Moggy