Er, the XH-59 (Sikorsky S-69) wasn't even ordered until 1971, two years after Cheyenne was cancelled. And it was a pure research aircraft, nothing to do with any armed helicopter requirement. This was Sikorsky's first go at the Advancing Blade Concept, which is being used in the X2.
Sikorsky offered a totally different aircraft for the AAFSS competition that Cheeyenne won. The S-66 (Sikorsky's number, it never got a military designation) had an odd swiveling tail rotor but was otherwise very much like the Cheyenne, including relying on a single engine and a single main rotor.