Uhmmmm... welcome to a "no-so-popular" club, it is unusual to see a broken SL6 crankshaft, especially a forged steel unit.
It looks like yours failed right at a thin cross-section... but again, it is unusual to see this.

Just move-on... that is about all you can really do.
(and look a little closer at the crank you install in the next build)

Here is the last crank we broke. It also "cut-loose" while just crusing down the highway... with-out a lot of power on it at the time.
DD

I'm just glad I was able to find another fresh motor, and that my cam is alright, timing set, as well as the head and valvetrain. When it went, I had no idea what I'd find when tearing it down.
And a new pan is on the way so I've got everything lined up and now that it's two weeks this wednesday since it blew, I guess I could'nt ask for a better outcome. I was severely bummed to say the least, now life ain't so bad!

When I get everything back together and running I will pull the broken crank halves and try to get some good upclose pics.