does anyone know what this hole in my engine is

[jimmy57]

all the plugs I have ever seen filling those turbo drain holes on Volvo NA motors is rubber covered and aren't that hard to push in.
You may be able to used a combination of extensions and the right diameter socket and use a pry bar to push it in levering against underside of exhaust manifold.
The blocks were machined for turbo version engine but built up with the pistons and head for NA version.
Apparently not an uncommon practice with automated equipment as I have a John Deere tractor with plugged oil feed and drain for a turbo.

[drjeckle]

I purchased a new plug from the Las Vegas Volvo dealer. $5.90 with tax. The plug is nothing more than a soft plug. I am about the chang oil and will look at the whole thing while the car is in the air. Then I will attempt to design and build a tool to drive the plug into the hole from below the engine. I will post pix and results if it works.

[JDS60R]

Just use a socket and a hammer. Permatex makes an anaerobic locking compound . Clean the hole before inserting plug with compound