More weird stuff from the parts closet.
The on the left is one I've seen in Hi-Po engines. But it's not like I've seen dozens of lower ends exposed.
A long time ago I procured some Main Cap Bolts (C2OZ-6345-A). These bolts have paint or other weird finish on the stem. It rubs off.
But the bolt heads are a bit different. I'm more used to the version on the left. But the versions packaged in these boxes in the version on the right. Both have "FB" embossed on the head rather than the "F" I've found on regular 289s.