What's the difference between 41-902 plugs & ...

41-940 sparks plugs. I have set of 41-940's for a 93 Bonneville SSE with 3.8 that I'd like to use in my son's 91 PA, but the 41-902's are recommended for my 91 PA. However, there are a number of plugs that are common to both cars. I know we shouldn't reverse cross reference, but any help would be appreciated. Thanks.

BTW All plugs number mentioned are AC Delco.