Woah! let's back up the bus. #315 heads are 64 and 65 273 heads and require a specific intake manifold or modified 66 and newer small block manifold.
@JeffreyLee , you need to crawl underneath and make sure you don't see "273" cast into the side of the block. It sounds like the "It's a 318" is just a story. It wouldn't hurt to make sure.