Uh Oh !! Bad knocking !!

Something bad happened to my motor on the way into work this morning. I have a 408 stroker LA Small Block, 4-speed manual, relatively mild cam.

I really romped on it getting on the highway, really winding it out in second and third, and just before shifting into fourth it started making a horrible knocking. Shuddering with each knock. Oil pressure remained constant, no change in the air fuel ratios in either header collector. I did notice as I continued down the highway that the temperature rose just a little bit--maybe five degrees. It would run at idle but as soon as I would give it gas, knocking would start really bad. I don't know what has happened! Any clues??

I have MSD ignition with rev limiter set at about 5500 rpm. I hit the ref limit in second before shifting to third, and was about to hit it in third when the knocking started, at about 5400 rpm. It feels to me that the knock is in the top end, but I haven't done anything to try to confirm this. I drove it another ten miles to the parking garage in the city, taking it easy, and that's where it still sits.