Helicomatic hubs are a little like a modern freehub and cassette, except the freehub splines are spiraled so that forward pressure on the pedals snugs the cassette inwards against the hub flange. They're a little weird to work on but as I recall everything goes together alright.

I would take a moment when it's apart to inspect the bearing races and the hub body in general, and I would not advise riding it hard. I had a helicomatic rear hub implode on me many years ago. The hub internals disintegrated in a long descent and the wheel cocked sideways, jamming against the stay and brake. Good times.

BL