as PP said, you should be fine just replacing the trans mount. i would just make sure the motor mounts are not so shot that the motor is torque loading too badly. the two jobs can be thought of separately (motor mounts and trans mount) in what is needed to do them (i buttoned up the MM install and then went to the trans mount, as a separate issue).
you can see why i chose to use parts store replacements (and included the info on did about them); the poly stuff is pricey.
good luck and Fost, good advice to Slo65 - i would have recommended the same thing (people get tired of typing the same response over and over).