All 351C's are 28 oz/in imbalance. There are two size flexplates. Either one will work, provided you have the correct size bellhousing and converter.
The small one is 157 teeth. It uses a converter with a 10.5" bolt circle. Found on the small bell C-4 trans.
The larger one is 164 tooth. The converter uses an 11 7/16" bolt circle. The 164's are in large bell C-4's, FMX's and small block C-6's. Note that the C-6 flexplate is the same diameter, but has a slightly different offset. It will work, but sometimes you need to to shim the converter bolts with one washer under each stud to push the converter closer to the trans.
Two other gotchas to beware of: The 164 tooth was also used with the AOD trans. Be careful here. If the AOD was behind a 351W the balance is correct and it will work. If it was behind a 5.0L then the balance is 50 oz/in and while it will physically fit, it will pound the bearings to death in short order.
The 164 was also used with the 300 ci inline 6 cyl in trucks. It looks the same, but has no balance weight. It is 0 (neutral) balanced.
Later,
David Cole
<font size=-1>[ This Message was edited by: Dave C on 2/1/02 8:07am ]</font>
