Does it have any extra balance holes drilled in the crank or any heavy metal added? How about weights on the converter or an external balanced flywheel? The factory cut a big radius out on the outer flat surface of the back of the flywheel but a non factory balance job will just have holes drilled in the back or edges. If no on the above is found, I’d say you have an out of balance rotating assembly. You have not said if you have ran this combo and if it vibrates.