Jack, I've had the receivers and crystals for 4 or 5 years and to be honest I really do not know how to tell the difference. Help me out here. When I got them, I was still using an XL2P then I took the innards(same size) from the modile for the XL2P and transferred them to the 3PS. Then when the M8 came out they changed everything, so this is the history, but as far as dual or single, I really don't know. Are there any markings that would tell me, on the receivers or crystals?