Bought a 1974 Honda CB550, green gunk on rightside of motor?

Would you guys happen to know what that is?
He said the engine was rebuilt and only has 10 miles

Some sort of workshop spill. On the outside I wouldn't worry about it, just clean it off or leave it.

When iron gets rusty (oxidation), the color of the rust is brown.
When copper gets rusty, the color of the rust is green.
When aluminum gets rusty, the color off the rust is white.

That being said, oxidation to any metal surface pits the metal (makes it porous).
When gasoline dries up, it leaves behind a green colored residue.
Any gasoline that was left on the metal, seeps into the porous material.

The metal has to be polished, to remove the green stains.
http://www.amazon.com/...0002YUQ4E/
Very time consuming without a buffing wheel.

If the pitting is extensive, the metal should be sanded smooth and then polished.
After polishing, the metal will shine like chrome.
Professional quality buffing wheels and polish.
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If the covers have faded in color, it's because the engines were sprayed with a clear coating.
The coating has to be buffed off.
Whenever you polish aluminum, the metal has to be protected with wax.
Otherwise it will dull easily.

I'm not sure but my guess is that rather than buying new gaskets the rebuilder used instant gasket, possibly because original gaskets were not easily available.