Could always send to Metalligraphs for authentication. I'm not sure about it... looks as if the three signatures in the center were done by the same hand.
As "Cliff" is on it and it is a copy of MOP it must be signed in 1986.
1986 Kirk and James isn't even close to that. Not later either if the seller would claim he got "Cliff" in 1986 and Kirk and James sometime afterwards.
They do somewhat resemble 1983 Kirk and James signatures, in fact I think they may be copied off a KEA era photo over at Metalligraphs.com