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