Smith: I hope that "squeal" you heard wasn't the sound of dry bearings running against the bearing journals. That's probably what it was. I heard the same thing from my engine when flying . . . in an airplane. Problem was
oil starvation at one journal due to debris in an
oil passage.
Your engine problem may have been as stated, causing total
oil starvation. If the pressure regulator valve stuck, a dash of Marvel Mystery oil may loosen it, but I recommend you drop the pan . . . it's easy on a Cobra . . . and remove the pump for inspection. Also, remove some rod-bearing caps and check the bearings. This can be tricky with the top bearing. Rod bearings will be the first to suffer from oil loss. If they are wiped, you've found the source of your squealing noise. Look at the bearing journals, too. If they are in good shape, you can install new bearings . . . very tricky without removing the engine. The top bearings can be rotated out of their bore by pushing on the end opposite the tab using a small screwdriver and a lot of finesse.
If the rod bearings are badly wiped, you should also check the mains. One the other hand, if the crank is damaged, you'll have to remove the engine and go from there. Except for the rear main, these won't be too bad to remove, but you won't have to if the bottom bearing inserts look OK. Otherwise, it's remove the engine time.
But if the bearings look good, replace them and don't forget to torque all the bolts to the correct spec. This can be somewhat difficult . . . that's an understatement . . . if you have to check rod-bolt stretch.
I'm telling you this after I just went through my 427 S/O because of a spun rod bearing. This is a long and expensive story because of the need to buy a new crank, custom pistons and much more. I think and hope yours won't be anything like what I had to deal with.