Correct the timing. New noise gone? It was an issue. Noise in conjunction with your problem is somehow a factor. Was it this?

Only way to find out. Check the chain tensioner carefully as well. You will have to remove it to move the chain over the cam sprocket I suspect. I was having some issues with the cam sprocket moving ahead until I thought a foreign object. Might actually accomplish this.

It of course is possible the chain was put on wrong when it was installed. Although anyone that could change the chain should not have made that error. Yet you never know.

I never owned a 603 engine yet I think getting inside the oil pan is easy. I would tend to check in there if the engine is quieter at idle after the timing is corrected. Or back to what you remember. Finding anything it there would be a red flag over going right back into service. I also wondered if a ball bearing or part from their problematic vacuum pump might have transited up and over the cam sprocket in the chain. This could move the cam sprocket I suspect. I would remove the vacuum pump and check it before starting the engine again as a priority.

Other approaches will vary. Remember I am not a working mechanic. I only try to express what I would do. At the same time if you have lost a ball bearing out of your vacuum pump or more. You are a lucky person. The original vacuum pumps with no bolt heads on the front can create real issues with these engines. Personally again I would not run this engine at all until the vacuum pump is checked. If it has lost some of the ball bearings it also could be a new noise. Although I do not really know that. It is wise to find a vacuum pump anyways that does not have a smooth face. They have sealed bearings. The original ones are not to be trusted. Perhaps I am too cautious. Being as old as I have become.