Looks like everything said about om621/615/616 pneumatically governed applies here.
26 deg. BTDC(for engines with injection timer), compression stroke , drip tube method.

Make sure the IP lever is on operation position (IP rack pushed towards full delivery)...and the IP timer is not stuck somewhere in in-between position.

Page 34-
https://docplayer.org/20746195-Allgemeines-daimler-benz-aktiengesellschaft-abteilung-kundendienst-motoren-7000-stuttgart-untertuerkheim-postfach-202.html

-click on "download document" to get the pdf.

Also check out (Early Model Years vol.2) :
Mercedes-Benz Ponton Books / Manuals / Literature / References / Acknowledgements www.mbzponton.org

There should be a diesel engine manual in English in the .zip files

There used to be an English .pdf document on om636 that circulated freely for years but it seems now it is either for sale (good grief)...or hosted on unclickable sites (viruses etc.).

The thingie under MB part number 636 589 01 23 00 seems to be used to lock the IP camshaft but I think one can do without it (although I might be wrong).