What is this and why would it be there?

I've got the numbers matching motor that the previous owner said it has a spun bearing, but I'm not sure I can trust much of what he told me. I'm going to dig into that motor to see what it looks like. I appreciate all of the knowledge that has been shared and would appreciate any guidance on the best route for a build on the origianal motor if no serious problems are found. I'm looking for a healthy 450 horse street motor with mid range torque - any thoughts? Cost is always a element but I'd do the right thing for the best result.