Comp,
I have seen this on multiple Jabiru engines and to some extent every Jab engine that I have stripped, the culprit historically has been the barrels being out of round from overheating and unequal cooling, the only fix is a full top-end. One engine had only done 100 hours!
On a side note, whoever does your topend, ask them to finish hone the cylinders with a dummy head torqued down, another common issue is cylinder distortion at the top of the stroke due to the head bolt torque, I see it on every jab cylinder.