Hmm... my CD manual is makes a reasonable distinction between nozzles and delivery valves. Check out procedure 07.1-210.

The 603 uses the same delivery valve splined socket as the 617. It's available from many on-line sources for $20-30 if I remember. No way around that. The 6 point socket for the nozzles probably refers to a 27mm deep socket for what the forum calls injectors. I use the cheapest socket I found at Home Depot with no problem. But that's neither here nor there since you don't have to touch the injectors.

If you can't manage to work on the delivery valves with the intake manifold in the way, consider other things to check while the intake manifold is off. Things like the stop valve, glow plugs, injection line clips... I don't know what the manual calls these items

Sixto
91 300SE
87 300SDL
83 300SD