As Dan says it’s the 1.6 K4M engine in your Scenic.
When the timing belts go on these engines because the valve stems are so weak they just get bent out of the way causing little other damage. The chances are that most of the valves are likely to have got bent.
I'm working on a 2003 Scenic at the moment that I bought with a snapped timing belt it has the 1.4 K4J which is almost the same as your 1.6 K4M the main difference between the 2 engines IIRC is the length of the piston stroke.
I have just bought everything I need to repair a 1.4/ 1.6 engine for £137 that’s a timing belt kit, Head bolts, Head gasket kit & 16 valves. I didn’t pay for P&P as they are not to far from me.
I have used Trechii on several occasions for cylinder overhaul kits and they are one of the cheapest suppliers. I have never had never any problems with their parts
http://www.trechii.com/products.asp?cat=274
As well as using a TDC setting pin and cam shaft locking bar it's advisable to use a cam shaft sprocket holding tool if removing the cam shaft sprockets. If your engine doesn't have VVT which means you won't have a dephaser pulley then it will be possible to remove the upper cylinder head cover with out removing the cam shaft sprockets. Thought the sprockets will have to be removed from the cam shafts to replace the cam shaft oil seals.