Iam not 100% clued in on n42 timing but this has worked for me in the past on other cars.
Get the bottom end to top dead centre. I.e take out plug in cylinder 1. Put dipstick/steel bar down into the hole it will rest on top of piston. turn engine over by hand until the dipstick is at its highest point. Wip the rocker off and i think there should be some markings on the ends of the cams closest to the fire wall. Also when the rocker covet is off check the chain to see if it's slack.