The Rule of Nine....
That is the method devised by the British for adjusting valves. Any of the British shop manuals, whether it be for Triumph, MG, Austin or whomever, all suggest using the Rule of Nine when performing "tappet" adjustments.I go through it every spring and fall with my TR6. Not hard, just as you stated, check valve #1 with #8 open, 2 with 7 open and so on and so forth. As so many of the English powerplants are OHV, there is a marvelous tool called the Clickadjust which makes checking and setting clearances a snap.
To properly perform a valve adjustment on a Mercedes diesel, you will need the three special wrenches (one for loosening the locknut, one for turning the adjuster nut and the third one for holding the valve spring collar). They can be had through any of the German tool dealers such as Samstag Sales
http://www.samstagsales.com
On the old, pre-hydraulic lifter gasser engines, there is a special crows foot 17mm used to turn the ball stud to set the clearances. That is also available through Samstag or through any MB dealership.