Just so the OP can visualize the differences

Click image for larger version.  Name: BoltComparison1.jpg  Views: 31  Size: 30.5 KB  ID: 8833
Pre-1966 bolt is on the left, 1966-present is on the right


Click image for larger version.  Name: BoltComparison2.jpg  Views: 30  Size: 31.3 KB  ID: 8834

Pre-1966 on top, 1966-present on the bottom
Note that the bolt head retaining pin was re-orientated 90-degrees in relationship to the lugs with the change between the two.