headers for a slant six

Hey everyone, I have a '72 Swinger with a 225 slant six. I am looking at installing two piece headers on the engine. The website which provides the headers also provides an X pipe or Y pipe. I am only interested in staying with a single exhaust, so do I order a Y pipe to go into a single tail pipe? Does an X pipe really have much of a power advantage and if I get one, does it require dual exhausts? Thank you for any replies.