Bramble,
Great photos mate!
It is very interesting following these projects and being able to watch them come together.
Thanks for sharing.

Regarding your regulating method, I've seen this done on a few doubles here in Oz.
It can work, that's for sure, and I personally know of at least one double that is a very good shooter which was regulated with a similar device to yours.
There can be problems associated with this method as well of course.
I hope it works well for you and please keep those great photos coming!