Speaking of plans for cutting circles out of plywood in 1970, this popped up a few weeks ago on retronaut, and then I lost track of it. It's called Turniture II, a 4-in-1 convertible outdoor furniture project by architect Lester Walker, which was published in the July 1970 issue of Popular Science.
So it's an adult-size rocker that a kid will fall out of within seconds, a picnic table they're counting twice by relabeling it a "playhouse,"--and a bar. I guess we don't need to be a stickler for math when presented with a playhouse that can be turned into a bar. Carry on!
[Uh-pdate: Whoops, I checked, and the Tank Chair, the two-person, ply-with-circular-cutouts rocker designed by Ant Farm co-founder Doug Michels and Bob Feild was on the cover of Domus in 1968.]