OK, thanks to the hints of other posters I figured it out:
I don't remember if it was JFP or jaykay but someone said that there is another opening for a sensor on the other side of the engine and after initially looking at the wrong place I finally found it
On the first picture I point to the location of the opening (this picture was taken after I already had installed the oil temp sensor). It sits way below the fuel rail (much deeper than it looks on the picture) and is also hidden behind several electrical lines (and yes I have to clean my engine):
Basically look for an oil drain plug on top of the engine (I forgot to take a picture while the plug was still installed, but this is how it looks):
The bore is the same as for the oil pressure probe: M14x1.5
Closer shot of the installed sensor, in the upper left is the air filter and the lower left the MAF:
So I ordered from Pelican: 323-055-M82 (temp sender, I would advise against a sensor which intrudes deeper into the engine) and 310-012-M82 (VDO Gauge).
I spare you the detailled description how to route a cable from the engine to the dashboard (basically I zip tied the cable to the tube between the airbox and the throttle body and after that to the big cable which goes through the rubber grommet in the firewall, from there under the center console and voila)
I compared the readings on the VDO gauge vs. the reading on the Durametric and the readings are spot on within +/- 2% of the readings from the Durametric
Enjoy