My dad purchased a boat that came with a SBC 350. IT's not a merc, looks just like the typical SB you'd find in an old muscle car. Were changing the oil and i'm curious as to what weight oil would be good to put into it since we really know nothing about it. As far as we know, this engine is in "stock" form and it sounds like it too. I'm thinking 10w30 Mobile One Full Synth. Thoughts with out beating this to death?