That's a negative ghost rider. Both mounts went on my dart at the same time about 5 years ago and I didn't know it untill we (me and dad) found that the clunking noise was the alternater hitting the passenger fenderwell due to the engine sitting on the k-frame. Two jacks (one for the car, one for the engine) and some hand tools had the mounts swapped and the issue addressed in about 4 hours. The engine never left the car.
Change your mounts ASAP before you do some perminant damage to your driveline.