Flywheel??

hey everyone hopefully this is the right place to post this but I've been looking for a flywheel. I have a 68 273. I could get one new for almost 300 bucks but I've been shopping around on Craigslist. But quick question, is a 318 and a 273 flywheel interchangeable?? I've done some research and a lot of people say it is but I rather trust you guys.