Jim is correct. The progression on oil filters used on the BOP motors was PF7 to PF30 to PF24. The white AC filters are period correct. The blue ones are newer. Brand new production AC filters are horrible. The quality is very poor and the materials are much thinner. I use the Wix 51409 on my later Olds motors, but I use the 51258 on my 215 as it seems to fit better. The 51258 is slightly shorter. And I think most people know that NAPA Gold are just Wix filters in a different box. NAPA part numbers drop the leading “5”, so Wix 51049 is a NAPA 1049.