I've got a 59 261 and after mocking it up found the pistons to be .060 below the deck. I'm just wondering how much can I have milled off the deck? Even at zero deck height piston to head and piston to valve clearences will be just fine. I want to get the compression as high as I can but .060 seems like a lot. Will the block tolerate this much removal or should I go with just .040 off the top?

in all the motors i have built i would only take off as much as had to. to get if flat about .020. that way you have something left in case you have to make it flat again. something to think about with 261 blocks not growing on trees any more.

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.