Apparently, the patent for Breslin locking ('split-lock') bolts has been acquired by Percy's High Performance. They carry the equivalent sizes of the Breslin bolts for 3400 and 3500 headers:
Breslin# Percy# Quan. Thread Length BoltHead Finish
008-026 20008 12 8x1.25 25mm 3/8 (12 pt.) Black Oxide
608-026 21008 12 8x1.25 25mm 3/8 (12 pt.) Stainless
For more info: www.percyshp.com, or call them at 1-573-346-4409
HTH
Breslin# Percy# Quan. Thread Length BoltHead Finish
008-026 20008 12 8x1.25 25mm 3/8 (12 pt.) Black Oxide
608-026 21008 12 8x1.25 25mm 3/8 (12 pt.) Stainless
For more info: www.percyshp.com, or call them at 1-573-346-4409
HTH