360 vibration issue

The balancer was the problem initially, a 360 is externally balanced where a 318 is internally balanced. That is the correct flexplate though.

My cousin had a mustang that had a bad vibration, spent hours trying to fix it, we though it was the cross-member for the trans because it was upside down, that helped a bit. We ended up pulling the motor out, 2 main bearings were finished. The crank was bent or something, no idea how that happened. But if it was vibrating for all those years it may have damaged the bearings and crank. Not 100% sure though.