Early hipo 5 bolt

<font face='Comic Sans MS'>Before the change over which IIRC was Sep 64, all 289's were 5 bolt blocks.</font id='Comic Sans MS'>

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All HiPo blocks made prior to Sept of 1964 were 5 bolt blocks. These were blocks used in production cars..Fairlane, Mustang and Cobra. This is clarified in BoB Mannel's Book

The early Fairlanes were 5 bolt , my 64 Fairlane S.C. K code was built on Oct.7 1963 and it is a 5 bolt.

What is your sequence number on the block pad as Bob is building data?

The September 64 date is wrong. All 1963-64 Fairlanes were 5-bolt -- without exception. All the 1965 Fairlanes HiPos were 6-bolt -- without exception. Mustangs are a bit more difficult because they ran over the 1964-65 production change. If you have a 64½ Mustang (they began in June 1964 and ran through July), you have a 5-bolt HiPo and a generator. If you have an August 64 or later HiPo, it's a 6-bolt with an alternator. I verified one Mustang that had a scheduled build date of August 10, 1964 and a 289 HiPo assembled on August 4, 1964. It was a 6-bolt 289 with alternator. The transition between generator and alternator was July 31 for the last generator and August 3 for the first alternator. In between (August 1 and 2) was a weekend.