Kamandi and OMAC were both Jack Kirby creations - the Last Boy on Earth appeared two years before the One Man Army Corps, but in 1977, it was revealed that Buddy Blank had been the grandfather who raised Tommy in the bunker. Of course that was after Kirby had left the book, so the odds of it being the plan all along are pretty much zero.
Anyway, grandpas are grandpas wherever you go, and there's no grandpa more grandpa-y than Abraham Simpson. And rather than use the more familiar "tied an onion to my belt" speech, we went for one that was just as funny but slightly more obscure. This one is from Season 5's "Lisa vs. Malibu Stacy."
Oh, and Kamandi saying "sigh" was inspired by this Comics Curmudgeon post.
OMAC: ...a box of mint-condition 1918 Liberty-head silver dollars. See, back in those days, rich men would ride around in zeppelins, dropping coins on people, and one day I seen J.D. Rockefeller flying by, so I run out of the house with a big washtub. I'd just used it that morning to wash my turkey, which in those days was known as a walking-bird! We'd always have walking-bird on Thanksgiving, with all the trimmings: cranberries, injun eyes, yams stuffed with gunpowder. Then we'd all watch football, which in those days was called baseball...