Dry sump 260 / 289 ?
I have always thought that those holes in these newer castings were redundant detailing off the original ZF 4-bolt bell housing 7/5351 which was used in the days of the DOHC 255 engine and this had a full length and width alloy dry sump. The casting has two screw holes at the bottom of the rear end.
The Hewland bell housing for the 255 engine has a similar two holes.
Then again I am assuming the other bolts holes on both engines had the same geometry !