You do not need a part number. Measure the hole in the block and go to NAPA. There are two styles of plugs. Concave and Cup.
You will need to super clean up the surfaces where the plug fits. The plug sealant that you should use is
https://www.permatex.com/products/gaske ... nt-liquid/ Do not use any other product. Do yourself a big favour and disregard the sure to follow suggestions of other sealants. This Permatex product is non reactive. It is not necessary to buy a higher priced brass plug when steel is available. You do not want to introduce another metal into the cooling system. Dissimilar metals in the presence of an electrolyte will make a low electric current and corrode the plugs. If you allow the coolant to deteriorate it will become an electrolyte .
I am attaching a picture of how I resurfaced the holes in the Old IHC LB engines I freshened up.