One rod failing on a 216 shortly after a rebuild is probably a "preview of coming attractions" unless you (or the rebuilder) took the time to aim the spray nozzles in the oil pan while the engine was apart. The troughs under the rods are only there for lubrication at idle. Once the engine speeds up and the oil flow increases, those nozzles squirt a stream of oil all the way across the oil pan. If one of more of them aren't aimed properly, the stream of oil will miss the dippers, and the rod bearing will be starved for lubrication. There is a very scarce fixture that's used to aim the nozzles, but there's a very effective "shade tree" method to accomplish the same thing. Remove the oil pan and clean it thoroughly, then scribe an "X" directly across the pan from each nozzle, at the same height. I use a carpenter's square at the pan rail to establish the location. Attach a garden hose to the oil pipe and turn the water on. Bend the nozzles until each stream of water hits the X. Clean and dry everything and reinstall the oil pan. Now the rods will get lubed at cruise speed as well as idle.
Jerry
