The original stop rotor project was the Sikorsky S-72,with ejector seats and an S-61 dynamic system initially.Two were built and at least one flew in fixed wing mode ,using its ancillary stub wings etc but they never pursued the actual rotor design to the flight stage.
More recently Boeing has been developing the X-50 Dragonfly ,which was a scaled RPH but again was abandoned when they kept running into control difficulties.
Personally I think the tilt wing is a better bet!