poly motor and trans mounts are way harsh for a normal everyday driver. i have had them in a few vehicles and always ended up taking them out and swapping back to rubber. if you have good stock mounts in there, you won't get enough engine torque on take off to mess up your exhaust system but if your mounts are bad, even the transmission one, you could have twist issues which could ultimately lead to your engine dropping.
it happened to us on the wife's 93 sahara a number of years back. her bolts broke though and the engine twisted enough from a stop light to drop in between the rails and smash the oil filter. if my wife would have been driving, it probably would have not ended well but i was driving so i immediately shut her down.