Can anyone please advise me what is the correct spark plug type for my Packard.

I own a 1930 Packard 740 super 8. I've been running a Champion W20 (stock number 520). What I don't know is, is this the correct spark plug type for my car? When I had the car restored 20 years ago the shop put the W20's in - why did they do that? I can not locate any records anywhere to help me determine what it should have.

I called the Champion tech department and they said I should be using a W16Y (stock number 561).
Max Merritt parts department calls for a Champion W14 (stock number 569). Kanter couldn't help me with a plug number but they say they sell spark plugs for my make and model...

I would like a to buy new modern plugs that are correct for my car.

The research I've done shows that an AC G10? is what it would have come with from the factory with.
I want copper, 7/8", spindal on top of plug to screw on a chrome nut and non resistor style.

Many thanks for your help!