Hi there,
when looking through the little hole on the left hand engine cover (over the flywheel) and rotating the crank anti clockwise you will see the first mark which is the full advanced timing mark then a bit further on you see the idle advance timing mark (I think these corespond to 36 degrees and 12 degrees btdc) then you will see the mark which has a small T next to it and this signifes Top Dead Centre. You can confirm this by puting a (softish) rod down the spark plug hole and feeling for the highest point of the piston travel.

Clean the two bolts and the threaded holes of the cam shft with a degreaser (like carby cleaner or laquer thinners)

Now up the top end you put the cam shaft in with the lobes facing down (ie TDC on compression stroke, all valves closed). Now fit the top cam sprocket so that:

1. the left (front of bike) side is tight and the rear or rhs is slack (this is taken up by the tensioner.

2. the two lines on the sprocket are level with the top surface of the head (there will be one of the two bolt holes lining up with the one on the cam shft), there are two possible ways of doing this and both will work fine but to be a purist the half with the dimple up will serve as an indication that you are on the comression stroke (just in case you didn't notice the position of the lobes).

If the lines on the spocket don't line up drop the sprocket and move it to the next position on the chain. Depending on the wear on the cam chain they may not line up perfectly but the sprocket only moves in increments of chain links so there is only one best fit.

Put some strong thread locking loctite (something like 277) on the bolt thread and do the first one up finger tight. Rotate the crank 360 degrees so you can get at the second hole and do the same but torque this one up then rotate the crank again and torque the first one up. Depending on the book I have seen between 10 and 22 Nm torque for these bolts, I split the difference and used 15Nm.

You can also put a little grease on the bearing surfaces of the cam before you put it in. Make sure the mating surfaces are clean and oil free before you apply some 3-bond gasket goop.

Hope this helps, Dave