Do you mean the rubber unit between the cross-member and tranny? If that's the case, the stock c4 unit will interchange, if memory serves.
what he said... the new mount that was on my C4 bolted right to my T5, which was also used on an AOD at one point as well
I've also verified that the C4 mount will bolt onto a 5R55E 5 speed auto out of a Ranger and a SROD 4 speed. I'm sure it'll bolt on a C6, too.
I would recommend against the hard poly mounts for the transmission. It needs to flex a bit to keep from breaking the extension housing. It does make a difference on how much torque your engine produces and whether or not your engine mounts break. If you break an engine mount and it torques over then that rear mount tries to hold the back of the case in place - SNAP! you need a new rear housing or a case in extreme conditions.