An 86 cam is E5ZE-6250-AA. Mustang specific parts always have that Z in the 3rd spot.
I honestly dont think its a Mustang cam,.. well not from an 86. 'E3' would designate 1983 or later if that were a Ford cam. With no Z in the 3rd spot it wasnt specific to a Mustang.

I checked my little database and came up with nothing. Does the person you got it from have any idea?

Do you have the engine it came from? Check the block numbers and find out what it came from.

Hurst