In my humble opinion, I'd start with detonation as the cause.

The blower effectively makes the engine much bigger so high rpm are not required.

Now I am on record as saying the stock 440 pistons are stones or clubs and the rods would be MUCH BETTER with 7/16" rod bolts, but this doesn't appear to me to be rpm related. So that leaves detonation which is lurking around every blower setup waiting to bite you.

ANY 440 block needs to have cylinder walls sonic checked before you invest a bunch of Euros in it.

I'd suggest using a BCR main cap/girdle setup to stiffen the bottom end. Also, a half fill of the block will stiffen the cylinder walls.

I'd email Dan at Performance Only to get his take on cranks, off the top of my head I'd use either K1 or Scat over Eagle. If you really want to build strong, Crower is the name I'd drop. But it will cost you twice as much as a K1 or Scat.

Pistons need to be strong forgings designed for blower use, get with a piston manufacturer directly after getting some input on who. Also, wristpins need to be sturdy.

I think you will be able to run 700 - 800 hp with ease using all these good parts. But, if you have already spent $5000 on moving parts, does it make sense to use a stock block? I'd seriously suggest getting an aftermarket block. Then you'll be bulletproof.

R. (really good at spending other people's money)