The slotted nuts for the front hub are indeed hard nuts to crack - without the right tool you will not be able to tighten them properly.
Do not attempt any bearing job without the proper tools!
Unfortunately, Mercedes used three different nut sizes over the years and it is difficult to get the right spanner tool or claw wrench (Manufacturer is "WILBÄR" in Germany). Sometimes they show up on German ebay.
MB part numbers:
W460 589 00 07 00 €29.23 (early 460 - for spindle nut 460 990 01 60 )
W460 589 02 07 00 €70.81 (later 460 and early 90's 461 - for spindle nut A460 990 02 60)
> more about the difference here <
W463 589 00 07 00 €103.43 (all 463 - for spindle nut N07085 203 00 00)
A workshop manual for front and rear bearing jobs is available.
Proper fit of tool and slotted nut:
You may have to carefully use a file to narrow the teeth if you have the old 589 00 07 00 tool with wider teeth (notice the file marks on my spanner) for the new 990 02 60 nut. The original 990 01 60 nut is no longer available. You can also use a pipe of good quality steel to cut out your own tool.
A good tie rod separator is essential for the front wheel bearing job (with a chisel type separator you will damage the rubber cups and they are not replaceable) MB part number 601 589 04 3300
Aside from these two specific tools a front wheel bearing job can be done with any commercially available tools (bearing puller, hydraulic press, torque wrench, etc)
Tool tips on helpful German site