Lycoming Serial Number and Broken Cooling Fin

[Corvus]

I'm trying to track down the history of the engine in an airplane I just bought.
1) The engine has no dataplate; I know from the crankcase part number (71357) that it's an O-320. What I need to know is the suffix (-A2D, etc). Where is the engine serial number stamped on the engine? Lycoming has a online search tool.
2) Cylinder #4 has a broken cooling fin. Thoughts on repair for this? Picture attached.
3) Spark plugs are an obsolete Champion REM37N. Replacements???

 

[TFF1]

 

[72878]

 

[PittsDriver68]

 

[prothct]

 

[armstrong8933]

 

[EAABipe40FF]

 

[Daniel Hauf]

 

[PittsDriver68]

 

[Corvus]

 

[EAABipe40FF]

 

[race38]

 

[1 Albee]

 

[armstrong8933]

 

[1 Albee]

 

[armstrong8933]

 

[aviatoratrushgreen]