Gerald is right about the about the serial# range for the engine.
My Euro model 914/6 is #841, and on the COA I got for my car back in the late 90's it states my original engine# was 6400373.
The engine# you posted made me pull my COA to see if it matched. The numbers are pretty close. I've been looking for my number for 15 years.
I gotta believe it's still out there some where waiting to be found. Just not this time
Ron