I have an older fastener mfg ID booklet laying around (somewhere). There's two suppliers that used the stylized FF. I recalll Flying Forge was one, but nice to have it confirmed as a GM supplier. I've seen these more on 67's.
Most of the E's I have seen have smaller E's.
Yes, the seat bolts have the serrations on the washers. Never figured out why.
Lots of RBW, C, Anchor, and some E's on 69 NOR's.