All I know is both the left and right side mounts for the C5 Vette are symmetrical, and basically mirror images. We don't use the stock k-member mounts because the C4s never had LS engines.
The passenger side Corvette mount is casting #10260643 and the driver's side is #10260642. They can be reversed on the engine but then the cushion hole moves.
The GTO uses the #10260642 driver's side mount and a different #92056790 passenger side mount. Don't know why the passenger side is different.
Here's a pic of the GTO mounts:
I don't see how the mounts could offset the engine, though, depending on where you weld in the frame mounts. The bolt hole on the driver's side is the same distance from the engine centerline as ours is. So if we dropped an engine using those mounts in our frame and lined up the driver's side, the engine would be centered. Not sure if the passenger side would fit because it looks like it may be longer.
I think the GTO uses the same cushions as the Corvette, but we don't use them.