The head off and the pistons are out of the 4G63 in my Summit GTX. No broken rings surprisingly. One piston is very carboned up, another less so, and the other two are normal. Obviously the problem had been coming for a while, and I had noticed the unexpected high oil consumption, esspec under boost.
Measuring with a simple protractor gauge shows none of the bores are obviously oval. There are expected vertical scuff marks on the all cylinders, but the cross hatching is still visible. I'll get a bore guage into it tomorrow and see how much wear is present.
Piston-wall gap is the correct .020". The ring lands on the worst pistons are not obviously non-parallel, but the #1 and #2 ring vertical clearances seem not the same. The spec is approx .001 to .003, and .004" max: I'll check with a feeler gauge tomorrow.
With any luck, the bores are OK and a light hone is only required. Hence the problem is the old pistons. Given the amount of smoke it was blowing failure was pretty severe, so ring clearance is more important on the turbo engine.