Here's a vid of my first successful level bombing run in the Blenheim, although it may be more luck than good technique.
If you look closely in full screen @ 1080p you'll see the targets in the bombsight next to the factory.
You'll also see that I'm finding it difficult to trim the thing adequately. This might be me or the notorious G940 trim adjustments. The altitude and airspeed are going up and down no matter what I do!
Bombing height is 6000ft, roughly (!).