This is a video of some guys doing a lim job on a GTP. In the video it shows how they take off the motor mounts, the bracket that is left and be then used to help wratchet the car forward to get at the back valve cover.
I would look arround your vavle covers and see if you have any crud build up under them, if you don't then you may just leave them alone. I personally would just keep an eye on it unless the oil buildup was really bad.
I didn't think you already did your lim job , and if that was the case it is really easy to do the valve covers when you have that appart.