I'd recommend buying one which has everything on you wish to have as sourcing parts like 3 point linkages is not cheap. If you see one on ebay, get in touch with them and go and see it as most people will do a deal off ebay to save their fees.
My 406 was a right sight but ran, moved and that was it, the rest was a gamble but the person I bought it off had loads of spares in boxes for it so I assumed it had come from a good home.
Worst thing with mine was the muppet who took the cab apart cut through every single wire rather than unplugging / undoing the harness, even the wires in the harness right next to the plugs which go into the clocks so close that you couldn't join them easily, all because 'he was going to make his own harness'.... fortunately I found a genuine 416 harness for a bargain price and bought a genuine ignition switch so plugged everything back in again.
Strange thing is that everything I seem to buy is near Brighton and I live near Alton Towers so it's always a trip to see them but it's worth it.
Do you know what you want?
Ed