Thinnest (SAFE) cylinder thickness

I think for 500 you're ok. If you expect to surpass that I'd find a thicker one. My own limits are for 500 or less: major thrust thicker than .180, minor thicker than .150, pin axis thicker than .100. For 500+ I want to see major thrust .200+, minor .180, pin axis .120. Generally - the higher horsepower levels may need 1 or 2 sleeves to meet that. It is rare that a factory block is cast consistenly that well. I'll add the sonic testing should have at least 20 spot tests and preferably 4 "continuous sweep" tests per cylinder. One test in each direction doesn't tell you squat.