I have +.030" on my Royal Star although the pistons have the part no. 68-439 which isn't listed in the parts book but they also have 1.00 m/m oversize stamped on the top, which as we all know is wrong as 1 mm is 0.039".
They are also date stamped as August 1972. As this 0.030" bore is nigh on perfect, and the pistons show signs of being seized at some point, my guess is they are second hand and previous owner had to get what was available, or go to 0.040"
I would recommend 9:1 pistons as the motor is far more user friendly for what we want these days.