The piston is largest at the skirt (90 degrees from the wrist pin bore) so that is where you must slide your feeler gauges under (carefully) to measure the clearance. Do so with piston at the top of the stroke, in the middle and at the bottom of its stroke. The crown is much smaller diameter than the skirt is, that is normal and necessary, so don't measure there. A proper boring procedure means the person doing the boring and honing should have the new piston in hand while final honing the cylinder in order to get the proper clearance. Is the clearance within Wiseco's specifications now?
As far as oil suddenly flooding the exhaust... you'll have to figure that out cause we can't see or touch it from here.
The reason I asked you about scrubbing the cylinder is because after machining, the bore is loaded with grit. It can appear to be clean... but if you put the motor together without a thorough scrubbing of the bore the new topend runs in that grit continuously and can very quickly wear everything out.
At this point it may be a good idea to have someone inspect (a qualified professional machinist, very few really are) all of your motor parts and advise you.
