You won't need to remove the motor mount to remove your rear manifold. Remove the alternator and the rear cover bracket.
If you want to remove the motor mount, simply support the engine with a block of wood and unbolt the mount. I found it easier to use a floor jack with a piece of pipe up against the mount engine support, in order to raise the engine enough to remove the rubber donut. You may even have to unbolt the bracket from the engine to remove it completely.