Can someone tell me the difference between a i6 flywheel and a 351w? Im swapping a 351w for a 300 i6 and was planning on using the flywheel and starter from the 351. Thanks

 

The 300-6 flywheel is neutral balanced, no offset weight on it
The 351w has a 28.8 (if I remember correctly) imbalance.

You will need to find a flywheel for a 300, unless you have the 351 re-balanced. It will cost you more than a new one though.