I think I heard once that if you had actual NOS or assymbly line parts, one isolator was different/thicker than the other. In that case the parts book would show 2 different numbers and one for a right and one for the left. I do believe in the aftermarket they made them the same thickness (to save money etc.). Not sure if they split the difference or deleted one or the other.

If the ones you have are mopar parts with a pentastar and a PN, then the even number is the pass side and the odd number is the Driver side.