Stang's got the answer. Here are some shots, but I apologize for the poor quality:


The top manifold is from an '85 351W HO, while the bottom one is from an '82 351W - both are driver's side. As best as I can tell both the manifolds have the same dimensions, but the '85 is flat where the outlet is while the '82 has the bell to fit the exhaust pipe. The '85 requires the heat riser to get the bell, but the riser is 1" thick so that changes the Y-pipe.

Here's the heat riser, and note that the flange is not broken, but cut off:



So, like Stang said, plug the holes and don't look back.