You're right Fred, the carbs won't necessarily fall off, but they may crack the manifolds eventually, the rubbers are nice and thick on the mighty CB750, but it's common on other bikes like Z1's and big Suzuki's, I've seen it often.
I've just fitted F2 carbs on the K2 engine in my K1 (hey, it's a bitza, but I still love it!) but I fitted the OEM F2 airbox and filter, the K2 pods don't fit, but I was more interested in a brace for the carbs, the F2 items are lighter than the K1-K6 carbs, but the manifold ribbers are a bit thinner too, so more likely to crack. For that reason alone, I wouldn't recommend pods on a F2/F3 or K7/K8 unless you made up a brace. Cheers, Terry.