'86 300E, 91,000

After driving only a few minutes yesterday, I noticed what sounded like a loud ticking noise from the engine that quickly went away. A minute or so later at a stop light, it happened again. I decided to pull over an check it out. Just as I pulled over, the ticking quickly turned into a clunking sound. I shut the engine down and popped the hood. Belt and pulleys all seemed fine, there was no smoke or unusual smells, the oil level was right where it should be... so I started it up. A terribly loud clanging and clunking sound got even louder. I called a tow service and got the car towed to a mechanic. Unfortunately, they are closed for the weekend and I am left trying to figure out what happened.

Could the oil pump have stopped working??
Did a main bearing freeze up??
Is my engine fried??
Where do I start??

This is my 3rd Benz(both of my previous cars went over 200k with no major engine work needed. This car is (was) in great shape and has been a great service history. After driving 3,000 miles, the engine oil is still very clean. I can't imagine what could have happened.

Any advice would be greatly appreciated!

Thanks,
Paul