I use a 3/4 filled block, I add .002" to the piston to bore clearance but keep the ring clearance to the manufacturers gaps as per the application (blown/turbo/nitrous etc). Without the extra 2 thou piston to bore clearance I was seeing some scuffing on the piston skirts.
I've always used a light coat of mineral oil (VR1 20/50) on the bores/pistons/rings, and always will, never had a problems with that.
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