eaten up 2 flywheels in 2 yrs

what can be the cause of my 87 mustang eating up two flywheels in two years. changed the starter three times already. today when i try to start up my car i get the damned starter grind. i felt my heart sink. checked the starter bolts and both are tightened. ive been going through this ever since i bought the car back in 2006. the car is all stock with the exception of shorty headers which i just installed last week. would the motor mount or tranny mounts need to be replaced? because of all this trouble for the past years ive been forced to sit my car up and drive my girlfriends v6 99 camaro. i really need help on this one. i need my muscle back!!! tranny is an automatic.
(imagine going to your local store and come back out to crank up the car and getting that grind....embarrassing)

yeah i have the block plate in between the tranny and the motor. i counted the teeth before it was installed. was 154. and what about the starter? i have a mini starter lying under my bed but never used/ should i put that on when i get the new flywheel installed?