I tend to agree with BBM that the material is brittle. It may have just chipped out when the back lobes were pulled out and dragged at an angle across the front bearing. But the broken edges do look like the material is getting old.
OP: Is the engine still assembled in the car? Installing the cam bearing will be easy but removing the cam bearing will be tricky in that case; the standard tools are made to remove cam bearings with the engine apart. The problem is that those tools are made to DRIVE the bearings, not pull them out. Driving it out will put the cam bearing INSIDE the engine. You might be able remove the bearing:
- Stuff the area behind the cam bearing with large cotton cloth rag to catch the bearing and also to catch any more bits that come off the shell
- Use the tool to drive the bearing back. Or, using a punch with a small round end on it, tap on the edges of the bearing to drive it back; move around and around the bearing's edge and tap, tap, tap it out to fall into the rag.
- Reach in and turn the bearing side ways and pull it out; the steel shell will have to bend a fair amount; you may have to get a loop of welding rod or something similar around it to get enough force to pull it out this way.
I HAVE NOT DONE IT THIS WAY SO CAN'T TELL YOU HOW HARD THIS WILL BE. I am just trying to come up with a way to do this in the car. And the oil valley slot between #1 and #2 cam bearings is too small the pull it up out of the top. So the real trick is how to pull the bearing out....
Something like a pilot bearing removal tool with fingers that reach in and hook around the circular bearing and pull it out with a slide hammer type of action would be better, but nothing for that size is coming to mind. I can also think of ways to make a thick flat washer set that can be put in and turned to catch the bearing edges and pull it out, but that requires some fab work; that would be the best home-shop way to do it. And you could carefully saw a slot in the bearing, being careful to catch the crap (That's the trick!) and not nick the hole too much; once there is a slot in the bearing, the tension will release and it will come right out.
So with all of that.... I personally would try to pull it out, but if my skills were in the starting phases, then I think I would run it as it. I have run some waaay out of spec cam bearing clearances at high RPM's with never a 'known' issue. And since the main loading moves around between 4:30 and 7:30 on the clock as you look at the bearing, where the lifter loads bear onto the cam, that part looks decent; most of the material is still in that area.