Hi,
You can confirm if the belt has broken by looking in the oil filler, or taking the rocker cover off, and seeing if the valve gear moves when you turn the engine over (by hand). A new belt kit is £40 from the likes of Paddocks. This is a Dayco belt, tensioner and some gaskets.
Les's HOWTO details every step. It's for a defender 200tdi, but the disco engine is similar.
Most likely, the only damage is a few bent push rods, which are easily replaced.
You might need a puller to get the damper/crank pulley off. though IIRC, there are 2 holes in it, so you can use a piece of iron bar and 2 bolts instead.
All easily done with not too many tools. If you take your time, it's an easy and satisfying job if you've never done it before.
To time it, There's a dot on the cam, the pump takes a 9mm drill bit. The only think to be aware of is that there can be 2 slots in the flywheel. The woodruff key should be at 12 oclock when you have the correct slot lined up.