12 of the 16 aluminum intake manifold bolts removed from an original BB 396, 375hp engine have 3 head-markings with a flanged bolt head and the letters "F P". The other four are not marked and have washers. After searching Chevelle Tech manifold bolt threads, and other restoration sites, none mention this type of bolt. The most common found have an "A" on a 3 head-marked flanged bolt.
I believe the “F P” ones are original and would like to purchase four of these to complete the set.
Lou

Are the four bolts also attaching a bracket (engine lifting, etc) to the motor? If so, they could be longer than the others, and possibly different head stampings. JMO

BillL

No, the four odd bolts appear newer and held no brackets.