the 2 lower reticles are for the cannon i presume?
Yes, since the molins cannon has some degrees offset downwards, these two lines are meant to estimate the right angle and distance (the distance between upper and lower line should app. reflect the type VIIb tower height).
Two things we should keep in mind:
In real life the engines of the MKXVIII were throttled.
The molins cannon added 907kg of weight and it caused damage to the front fuselage on every shot.
Best regards - Mike