Bob Ball

HI Paul,
You don’t say if it’s ARTF or from a kit.
If its ARTF the bulkhead will have been buit in at the correct angle
If kit built it depends on the builder but it would have been clear in the instructions.
The offset depends on the length of the engine, the object is to position the mount
so that the back if the spinner is on the fus. centreline.
The thrust angle is imortant but the offset is just to make the spinner, cowling
and fuselage line up nicely.
Bob