I just bought my 392 used last year but my warranty expired. Soon after my valve spring went out and piston knocked the valve into the head and broke the crank bolt. I was thinking of boring the scratch out the block and stroking it with some new bigger heads, but what is the most I can bore the block without making the walls too thin? I have also heard the 6.4 is just a stroked and bored 5.7. Can somebody help me out?