70 Chevelle wheel codes - YA or AO?

Need a 14x7 spare for my 70 chevelle. Someone said to make sure you buy the right coded wheel. I see on Ebay lots of wheels, some say YA and some are AO. What is the difference? Don't want to buy the wrong type.

Thanks.

The part number for a 1970 SS is 3956744 it should be 14x7 and will be stamped JJ. Trim ring number is 3956775, and the center ss hub part number is 3956770.