Deck and Squared

I have a question about decking a sbm. What have you guys had to have removed in order to get the block square? Is 0.040" to much, what's a safe amount to have removed? I would hate to order a set of KB-167's and find out that the block needs a 0.025" to get it squared. Is there a piston with a 1.790" compression height? I was thinking about running the pistons at zero deck height for compression.
Not very often (never!) That I can offer any insight.
I put KB167's in my 318. Six of the deck heights came out at zero and two were a couple of thou down. I called that good.
I would do the mock assembly and hope you are as lucky as I was.