I took .050 off the deck of a 261 to get flat top pistons at zero deck more or less.There were no problems in 6 years of use.
Seems that flat top non GM replacement pistons are a ways down the bore at TDC,the stock GM standard pistons are around .020 below deck,don't know about GM NOS oversize pistons,probably very rare.


70 Triumph 650 cc ECTA current record holder