For rails you will have to remove the front cover ,generally these last fairly well into the life of the motor.Unless it' s of course been neglected.
But if your more after noises ,the vanos units themselves will give a low level knock sound when stuck,and sometime a fault which you indicate you have a timing reference fault.may indicate a need for that vanos
Then you'll need all the lock blocks and locater's
But look into the oil cap (if you haven't disassembled yet ) see if this is sludged over
Another indicator (quick) is remove the oil filter,if you see metal then the Bakelite is blown off the rails.
if that looks good ,oddly enough check the plugs when they are loose you get some odd noises like the cam is broke
for the timing fault move the intake cam sensor (swap them) see if it follows it ,they frequently go bad,( I'm only familiar with the BMW software codes so any other won't help me)
Hope this helps
Good luck with your project