The 50 OZ flex plate requires a different starter due to different diameter unless you got a trick one that uses early starter with later balance factor. The 28 OZ one uses a stock starter.
The harmonic balancer is specific to 50 OZ / 28 OZ too. Symptoms would be noticeable shaking all the time if both were wrong which I have experienced. If just one or the other were wrong maybe less noticeable at lower speeds but would shake more the faster you went.