Small Block Oil Pump Priming

If you pull the pan and the rear main you can tell if that plug you are talking about is in there by inserting a long rod down from the top where the oil pressure sending unit screws in. If the rod comes out the bottom of the block you know the plug is missing. Make sure the rod is longer than the block is tall so it doesn't by some freak accident get stuck in there. You may not even need to take the pan off. If you look at the back of the block you can see the outline of the two oil passages that come from the oil filter. This plug goes directly between these two passages. Measure down from the top of the block and you will know roughly how far the rod should slide into the block. If the rod goes a lot further than your measurement then your plug is missing. Hope this helps a little.