Last pics upside down.

65°yard, 60% slingpoint, 24% balance.

After having sailed quite a bit in my Ingeborg with the two halyard blocks on her yard 5 and 9% aft of the middle, I am pretty convinced that it would work even with the forward slingpoint block positioned 10% aft of the middle (60% position).

Now I made a try with a 65° yard and the slingpoint this far aft. I found that I could move the sail to about 24% mast balance (143cm from luff along the 5.90m battens). 

I would not recommend more mast balance without testing it in smaller scale. After all, the mast will dig in quite a bit in the cambered panels at this point.

In other words, I think it should be easy enough to produce a sail with between 15 and 24% mast balance.
Just tell me what you need.

Arne

There is maybe another option, without the split rig. 

With plenty of drift between slingpoint and masthead there will be room to fiddle. 

Plan B is probably a bit less nerve-racking than Plan A, too.

I was so excited to see SibLim when the hull was turned over.  It is really worth getting her outside just for that!!