Detecting piston/bore gaps while heated?

In need of more hand holding from real Nortoneer mechanics. I'm confused on ring gap and forged JMS pistons in alloy sleeved 920 Maney jugs, when boost heat/pressure held on too for a while. Everything I see on www uses full bore guages and micrometers to measure bore and piston separately while at room temp 75-ish F. Some example use a long band feeler to wrap around piston but it gets too thick a band for the max gap applications. Flat blade width jams to prevent true measure. Best I can figure is two sets of rod guages or small drill bits stuck in oppostie sides of piston. Do ya think heating with just free piston inside is ok or should the rod/pin be installed too in case that distorts/swells differently than w/o.? Some charts show up .1" clearance in Marine water cooled blocks and then theres the ring gap increase that goes along with sufficient bore clearance. If I find piston clearance too close would it be ok to take some off piston assymetrically? Temp charts show piston areas vary to over 500'F near crown so a couple hundred more that skirt bottom.