Oh my gosh, 69 grids? That's MORE than enough! Holy crud! How many guinea pigs do you currently have, and what genders are they? I'm absolutely certain you can make something to suit your needs. I mean, consider this. One 2x6 cage, which uses only 14 grids if you don't need a top. That one 2x6 can house up to 4 guinea pigs comfortably, being one ALTERED male and three females, or all females. Males do better in pairs, however, and need a 2x5 or larger to get along comfortably, which is 12 grids.
You can also make one really big cage if you have lots of females, and that would be 2x3 + 2x1 for every new guinea pig. For example, if you have 6 sows for some reason, then they could be in a 2x8. You can always go wide, too, and do a 3xwhatever. It's all in the square footage anyway.
And yes you probably could stack cages, but I have no experience in that. I know others have, so see if anyone else knows.
