Had the boat out about a month ago and it starting smoking and missing, tore the engine down ( .030 over 454 BBC) and found #4 piston melted and a crack in the cylinder wall. Engine shop seemed to think the meltdown was due to high compression with cast iron heads, running pump gas, and the recent addition of a thermostat kit. Had a sleeve put in #4, all cylinders honed (was able to keep it at .030 over), line honed, and the deck cut. Reassembled the engine using new JE/SRP forged pistons, new performer rpm cylinder heads, new camshaft, and all the other basic items. Fired the engine up today for initial break in of the camshaft with no problems. After running it for about 30 mins shut it down, decided to check the oil level and found milk on the dipstick, pulled a valve cover and found nothing but white.......shit. Pressurized the cooling system with air and found air leaking out of the #4 sparkplug hole......pulled the intake and cylinder head expecting to find a blown head gasket.....found nothing.....everything looks ok and I am really at a loss of what to check next......any advice would be greatly appreciated.