Engine rattle at startup

If you mean you’re going to check the ignition timing, whether that would help diagnose a loose timing chain depends on whether the ignition timing is based on the crank position or the cam position. On current era engines the timing comes from the crank position sensor, so a loose timing chain would only affect the valve timing, not the ignition timing.

OP, you’re keeping the engine oil in good order & topped off as necessary, right?

I change oil religiously but it either sat or was neglected before I bought
it. The initial oil change revealed an oil filter with a hard gasket. Hard
to the point it broke when the filter was removed

Yes I was, I had always thought the ar name was Willis-Knight , but it was Willis with a Knight engine. As far as I know, Willis was the only American company to use this engine but there were many luxury makes in Europe that used it. They were much quieter than poppet valves and were nicknamed “Silent Knights” but they burnred a lot of oil.