This is the Campagnolo mag-alloy wheel of an early Darmah, just like (well...) the ones on Hailwood's 1978 TT winner. By the time Ducati got their own "replica" in the showroom they'd chickened out of fitting mag alloys, after collapsing Speedline wheels destroyed a number of later Darmahs and 900SS. Despite the blame being taken by the nature of mag-alloy, Campagnolo's Darmah wheels never gave any trouble that we've heard about. So maybe it was the sharp edges of the Speedlines - after all, Campagnolo were awarded the "Design and Application Award" by the International Magnesium Association in 1975. In the end Darmah riders just got used to Hailwood Rep owners offering cash and a swop of their FPS aluminium alloy wheels for Campagnolos, in the pursuit of a bike more like Mike's.
Campag (as motorcyclists call them; the more sexually assured cycling set go for Campy) were true innovators - founder Tullio Campagnolo invented the QR wheel and Derailleur gears, and in motorcycling they designed conical hydraulic brakes and more. But it wasn't to be, and they settled down to make the best bicycle groupsets money can buy