T5 tranny swap

[sadlsor7]

I recently finished a 1965 fastback. I converted it to a T5 with a cable clutch. I used a 1990 T5 flywheel, clutch, and bellhousing. The engine is a 1970 302 I used the crank and ballancer from this engine. I now have a severe vibration in the engine [it is definitly the engine because it does it at while in neutral].Can anyone tell me if the flywheel off of the 1990 engine could cause this and what are my option for fixing this?