I'm thinking this is the remnants of an old bearing, but before I go yanking it off of there, can I get someone to opine on it?

This is the outer hub from a 911. Just want to double-check with people more knowledgable than I am.

Yes, that is a race from the rear wheel bearing.

Jim

That makes things a bit easier. Thanks!

...now I just need to figure out how in the hell I'm going to get it off!

I grind them thin with an angle grinder and crack them with a sharp chisel.

I insert a medium size properly sharpened chisel between the hub and the race and move it far enough to get a puller in there. It should be on there pretty tight, and that fit should continue all the way to the end. If it doesn't, the hub's no good.

The Cap'n

Eric (PMB)has a video on that exact thing at his website. He does it with a cold chisel.

Air chisel, as long as your careful and pay attention. Takes about 15 seconds.

I have always found that heating up everything on the stove makes it easier to separate.....

If you try that, make sure its really clean.
cooking car grease smells quite a bit.

You need leather gloves and have all your tools ready for removal also.

Wife never likes it....

Rich