Nice pickup Ian.
Here is the page you should be looking at to get a bit of info about it.
http://www.lathes.co.uk/faircut/index.htmlYours is the back geared and screwcutting version.
To sort your questions first. The second one first.
The lever you swung across and locked everything up is the backgear section. To get it to work properly on this type of lathe, you usually have to slacken off the screw that locks the belt pulley cone to the main spindle. The one you can see in the pics nearest the chuck is usually the one. No need to take it all the way out, just so that it lets the cone run free.
This should then allow the spindle to rotate freely without the belts turning, then when back gear is selected, it then brings the big gears into play allowing much slower speeds to be used, mainly for screwcutting or cutting large material. You should not select back gear unless the cone has been released. Some people use the back gear to lock the machine up solid, so they can remove the chuck, but that can be fatal for the gears, and if you see any missing teeth, it is usually caused by that action.
For the chuck, it will require a backplate before it is fitted to your machine. If you look at the 3 jaw, you will see that it is bolted to a plate that screws onto the spindle nose, you will require one of those backplates, as I wouldn't recommend taking apart your three jaw, as not only will you disturb the settings, it is doubtful that the backplate has the same register.
If you read one of my latest posts, it shows what I mean.
http://madmodder.net/index.php?topic=2304.0I hope this gets you on your way to understanding it.
Bogs