The kabuto (combiner head-gear pieces) simply fit over the individual bots' heads and aren't interchangeable between each other. The moulding on them looks terribly KO-like, but the plastic is as tough as nuts as I've had to use a lot of force to get Go Kenzan's kabuto into 'weapon' mode without any signs of stress marks.
My real gripe about these guys is that aside from the lights and sounds gimmick, there isn't really anything that justifies for the Voyager+ sizing.
Since all entire Samurai team was released in one go (no pun intended), perhaps tight deadlines partially led to drops in design quality. With the Shinobi team being released intermittently, I am having higher expectations.