On late-model 5.0 blocks, the lower row of head bolts (the short ones) actually enter the water jacket, unlike early 302 blocks where the holes are closed. Use a quality thread sealer to prevent coolant leakage. I've found the best choice is Permatex Form-A-Gasket 2 sealant. It remains sticky and doesn't harden. Other thread sealers have caused me problems, so you've been warned.