Logically, any oil burning must be coming past the rings or down the valves. If you've just had your barrels bored, provided they've done a good job, it sounds like the valves are worth a look. However, A10's often smoke a little bit on the left due to the oil squirting out of the left hand con rod eye which is drilled to ensure oil flow through the crank. It is also possible that the valve guides are loose when the engine gets hot. It might also be worth doing a compression test to ensure you have decent compression on both cylinders, much lower compression on the left may indicate that the boring wasn't done as well as it should be. If the smoke is tolerable it may be worth giving it a chance to bed in.