20 thou oversize rings won't fit on to standard size pistons properly, and if you get them on the pistons they won't go into the bore, and if you do get them into the bore, you won't have the correct ring gaps.
(I should have just asked "What are you thinking!!")
I knw a bloke who had a big end knock, so he had the crank measured and it was worn by just over 10 though, so he fitted a set of 10 thou undersize bearings without grinding the crank and was then surprised when he couldn't turn it over because it was locked up solid.
Currently over 35 years worth of fixing 35 boxes.
Hoping to reach 65 years worth of fixing 65 boxes.