I have a 64 galaxie with a T-Bird 390 4bbl. I need to find out if it has dual valve springs or not. I know it sounds crazy, but I opened the valve covers and can't be positive. It looks like a coiled plastic insert inside the valve spring and I can't tell if there is another spring beyond that.

Is there a way to find out by checking the engine stamp? Am I missing the obvious? Any help would be great. Thanks.