That's because the FSM expects you to use a slide hammer to remove the chain rail pins, which may require more space. And/or the radiator may need to come out if you are removing the fan clutch without the special tools. I don't think you'll need to pull the radiator if you don't want to. You may want get the fan clutch out of the way so you can easily access the front crank bolt for rotating the engine.

Pics of my cylinder head R&R on my 87 300D OM603 are at this link.