[LongBox]

If you disconnect the coil wire, then crank the engine, does it sound normal? If it does, I'd then do a compression test to see if the piston and valve action is correct.

If all that pans out, you might want to try starting it with the rocker covers off, to see if oil is getting up to the top, and isolate any sounds.

If you are the really careful type, you'll disassemble the engine, and check everything, including the stuff mentioned above. This is the slow, but possibly cheapest way to go.