[KTL]

Don't assume the engine mounts and transmission mounts are the same thickness of material. While the 915 engine and trans mounts are interchangeable, the G50 appears to have a trans mount of different thickness. My guess is based upon the fact that Porsche spec'd a different mount bolt for the G50 mount. Meaning, if the trans mount rubber was basically the same shape as the previous 915 mount, the mounting bolt should have remained the same.

The G50 trans is somewhat noisy, so i'd not recommend replacing with a higher durometer (harder) bushing material. Doing so will definitely transmit more noise into the cabin. If the material in the mount is still intact with no cracking or other visible deterioration, I would just leave it as is.

A good way to check/inspect the rubber mount is to clamp the mount in place, like on your bench vise or leave the mount attached to the trans (this assumes the trans is out of the car). Insert a rod of suitable diameter and ample length that will allow you to deflect the bushing material side to side. If by deflecting the bushing you don't see any cracking, I would say its still in good shape.