Got Steve Stratfold to put a second hand Billows front end on my old small Aeron carbon boom 145-190.
Also,swapped the Aeron extension over to a Fibrespar extension.
It did not fit as the arms of the Aeron boom were too narrow. However 10-15 blows with a rubber hammer did the trick.
Now non adjustable boom,only fits one sail. And I can't change the harness lines over.
With the extension fitting amazingly tight, it has added lots of stiffness

Saved quite a lot of weight taking all the clips off the boom and the extension.
Now the owner of the lightest carbon boom in the world,period.
Used it for the first time yesterday with my 5.5.
Previously the sail felt quite heavy with my 180-225 Fiberspar boom but now feels quite light,problem solved.