Always put some white out on the chain and sprockets. However, I just removed the head and left the chain. There's a chance of the timing gear slipping a link, and I did not want my valves to interface with the Pistons. So I didn't mark it, lined them up, then checked my IP timing.

To answer your question vaguely, line the marks and then adjust something else. the IP drops in with a mark to line up with tdc. The holes are elongated to allow it to rotate after and set the timing. Drip timing is somewhat non scientific and an art, so take your time and relax. If you haven't removed the IP, it may be on point.

Being a novice to this motor, and seeing it happen before, make sure your balancer is on right with the head off. Goto TDC and look to make sure #1 is at the top. It can happen.

On my motor there are pins on the balancer to place it. The ones mercedes sells now days are 4mm too long, and if you install them they can slip and eat the crank or split and rotate the balancer.

Like they said. Check valve timing with chain stretch. Probably buy a new chain and guides if you are in there.

A thing that surprised me (as a novice), the rocker arms go on the head after the chain and tensioner are in. That way you can roll around and slip them in.

If the heads off, you might want to have the machine shop take a look. For my 4 cylinder, it was only $225 in labor and $60 for all new guides. Unnecessary, only the exhaust showed wear.

If you do guides, turbo motors get brass and NA gets steel.