I have some prothane MM's but haven't put them in yet. Gonna do LT's, MM's, and CMDP's all at once. Reduce motor torquing which should put more power the rear wheels and help with the dreaded 2nd to 3rd shift.
Jack your engine up remove the old and install the new.
The stock motor mounts are liquid filled hydraulic type which are just fine unless you have higher HP like with a blower or turbo......too much drivetrain twist. Some longtube header manufacterers claim you should install them with the headers to keep them from possibly twisting up and hitting the floor pan. Mine didn't even with 11 lbs boost at almost 500 rwhp. Some do though. Motor mounts will also help keep the power to the wheels rather than letting the twisting drivetrain soak the power up.
Installation is not that bad. I remember the driver's side being much easier than the passenger's side. I had to remove the whole motor mount-to-engine bracket which meant jacking up the passenger's side of the engine. Not too bad though. Of course, I have longtube headers and that may have been why....don't remember.
As soon as the starter motor engages the flywheel ring gear you'll know you have installed poly motor mounts because you will hear a different sound now that the liquid filled jobs are gone. Not annoying at all though, just a noticable difference.
While you're under there put an MGW shifter in and you'll never ever complain about shifts again.