Well what hot rod Lincoln and Cletus say is right, what I would do is pull the 216 out and remove base, check the engine for wear and tear, 216 is a good engine and will give good service if maintained and run with in it's power range, the world ran on Babbitt bearing for a long time. On the 250 set up a good example is JoeH's truck http://www.stovebolt.com/gallery/hand_joe_1937.html
It's a 37 but shows what he did. the easy swap would be 235/261 six. If your going automatic transmission, your going open drive line and will be doing the whole whole thing front to rear, check out the tech section and a few other sites on the internet, check out hamb or hot rod sites, Jbennett