All cylinders filling with water

I bought a 68 Mustang Fastback 302 back in about 1973 when I was stationed in Germany. Motor just had the heads done but the owner couldn't get it to start. Went through it one Saturday morning, got it fire up, and took it down the street for a test drive. Looked in the mirror a little while later and had a steam cloud coming out of both exhaust pipes like you wouldn't believe. Pulled it back in the yard and found the same thing as you - water in all 8 bores. While checking everything over REAL careful, I noticed the tabs on the corners of the head gaskets sticking out by the exhaust manifolds?? Pulled the heads, turned the head gaskets over so the tabs were up by the intake where they belonged, torqued the heads back down, and went racing with it the next weekend. Couple of oil and filter changes in that time frame cleaned it right up.