1989 chevrolet suburban speakers

Does anyone know what size speakers are in the rear of the Suburbans. I think that they are 5x7 but i dont know for sure. When I do the speaker fit test on Bestbuy.com it says that 5x7's dont fit....any clue?

Does it say what will fit?

I'd guess 6x9 or 5.5/6" round. To be sure, pull the cover and measure. These computator things are wrong sometimes.