A bit of a puzzle
It's a familiar excercise; establish donor engine level on jig bed, not always plain sailing on modern engines with no obvious centre-line or vertical faces.
BMW's F800 engine makes it a lot easier with it's cast-in swing-arm pivot. We can safely assume this is exactly parallel to the shafts in the engine. As the picture shows, establishing level is a simple matter of slipping a piece of tube through the pivot bores and leveling that to the jig.
But this is a piece of tube from the scrap bin, locally aquired. It's one inch diameter, 14 guage. 25.4mm, a perfect fit in the BMW bores.
So why has this BMW got an 'imperial' dimension hole in it's engine?