Engine & tranny mounts

Maybe just go back to stock rubber mounts? Would be pretty cheap and easy fix.

Your local parts store can usually order them cheaper then a stang supplier. At least mine does in most cases.

I had poly motor and trans mounts in my '89 Mustang and I only noticed the difference between them and stock mounts at idle (sitting still). Are you positive that you are only noticing a characteristic of the poly mounts? I think something might be out of balance if you feel vibration going down the road. Also, if you have a built 408 you might have some strength issues if you run stock mounts. At a minimum you should probably drill through them and install bolts to prevent them from separating. I ended up with rub marks on top of my intake from the motor twisting on my '89, and it wasn't making a ton of power. I'd hate to see you dent your hood or scratch something after the stock mounts separate. However, if you want to run them, they are cheap and easy to find at most parts stores.