engine mount confusion

I have a motor and set of mounts that I pulled from a '79 cj which I intended to use on my '75 which is still nothing but a frame at this point. As I was looking at the mounts tonight and setting them in place I noticed that the holes don't match. The center dimension of the holes vertically is 2-5/16" on the mounts and 2-5/8" on the frame. How can this be? I don't recall this was an issue on the last V8 I swapped into a '75 and every aftermarket supplier of mounts shows the same part for '71 or '72 through the '80's or even later. Is it possible that this frame is actually a '70 or '71? Does anyone know how that would affect the mounts? What other differences are there in those years' frames I could look for?