I run an o-ringed block. It's all about who did the work and where they cut the groove. I had mine setup to run 1011-2 felpro gaskets. Do yourself a favor and stay away from the cooper head gaskets for street use. I have seen too many of them that seap. As stated above, just checkand make sure the o-ring is crushing the fire ring on the gasket.
93 Lightning t-trim @15psi a/a intercooled,Windsor sr heads, tfsr intake, 75mm tb,full fuel sys 72lb, Fast xfi, be trans controller,built E4OD 2800 stall,1-3/4 longtubes 3" exhuast Auburn pro 87 Lx coupe (in progress) 393 stroker coated pistons/bearings built 4r70w. Rusertmachine.com