also, the head gaskets looks to be about 1mm or more thick, way to much...prolly the old ones from the aftermarket heads... could the gaskets have a play in the ammount of compression the spring was getting?
Those are MLS 4 layer gaskets, they are stock height and are every bit as thick as a stock gasket is.
After looking at the pictures, I would go along with the new theory that the spring gave out and it didn't die from KR.
I had the pcm recoded to a lower shift point, it does not go over ~5800, or at least it shouldn't. I did this because I knew it would be running stock springs again. Now, if I had left it at 6400, I would expect a spring failure, because I did not, I didn't even think it would be an issue as it'* LOWER than DHP set'* their pcm'* for 1.9 rockers and stock springs (roughly same lift, duration and overlap is changed on the cam though). So seeing this, I am even more proud of that motor than I ever was.. it took the beating from the 3.1 and never had a problem.. seems a mechanical failure did it in.
Just a side note, the bonne ballancer IS different however isn't required. The GTP balancer will work just fine with that motor. The coil bracket is also different... and the coils on the bonne motor only have 30,000 miles on them, they were new off an 04' from Ed Morad.. use em along with the coil plate they sit on if you can.. same with the plug wires, new 04'* from 30,000 ago.
I forgot about the exhaust manifold being different, sorry.. the outlet port is moved to the side to mate with the exhaust.
I would start off with the 3.8, remembering this is a custom pcm. I had the timing moved back to stock tables also, so you should see nothing over 16/17. I would run it with the 3.8 to start off and get some scans done to make sure she is coo before giving more bewst.
I feel sad, but also releived that a spring failure caused this mess... I felt sooooo sooooo bad for having that 3.1 on there and thought it did the motor in... at least this ended up being something that was out of everyones control as nobody knows when a spring could fail, specially with lower shifts. I am still horribly sorry this all went down.... but... you will know that car inside and out now eh?
One last thing, I would think about keeping the aluminum dog bone plate that the GTP motor has for a motor mount, the one that is at the back of the engine on the front side, where it mates to the trans.... I would see if you can find a way to use that to add an extra motor mount to the system on the top... the little doughnut mounts the bonne uses now fail so easily, this is a good chance to have a way to build a stronger mount on top.
At any rate, keep us posted! That is some impressive carnage... and I can honestly say you can't blame yourself for beating on it on the way home... that had nothing to do with a spring failing.