The small bearings sounds like balls from the vacuum pump but unless the timing chain is jammed, the motor still will turn.

Is is locked solid or can you turn it slightly back and forth?

If it ran and the chain was replaced and it would not turn with the head off...My guess is that the chain is bound up between the crank gear and the lower oil pan. That it is a very tight area. I had a chain break on a 240D and that is where the chain jammed. IIRC it required removing the upper pan to get it free.

Good luck!!!

I think that the ball bearing assembly in the vacuum pump has disintegrated and not all the little balls have made it to the oil pan and one or more of them has the chain stuck down at the oil pump sprocket. That is how the little bearing balls get into the pan, but they don't always make it through. If it happens while the engine is running at normal road speed it causes massive failure in the engine as the chain will break, valves stop operating and you get massive damage.