It sounds like you're settling in on the blown application, reading the other comments, everyone is making sence, I do agree you might want to take it down a notch with a few of your expectations, like I said HP and speed just doesn't fall out of trees. As for a block, I know a factory 4 bolt main Mark IV block can hold up to about 800HP without starting to wiggle, meaning cylinder wall flex or cap dance. I used to have a 427 BBC GM block that made 771 naturally on alky, but that engine had 14.2:1 compression and allot of other nice goodies, but cylinder pressure is cylinder pressure no matter how you stuff it, and that's what makes power. In a nutshell an engine is a tool, fuel is the only thing holding the energy, the engine dictates how much energy can be extracted from the fuel and how much can you burn to push hard on the pistons. If budget permits I would go with a Dart big M splayed iron 4 bolt for the strength, remember the block is the foundation. As far as RPM goes with a 4.250" stroke holding rpm maybe at 6,000 that would put piston speed at 4,250 fpm, that's a moderate piston speed. Next, rod ratio needs to be looked at, a minimum .250 long H-beam rod needs to be used, making the rod ratio 1.50, whitch isn't great. A .400 long rod would be better bringing the ratio up to almost 1.54, that's about as good as it's going to get. Then hang those on a forged set of custom pistons with a raised pin height. See, there is some thought and planning to all of this if the end result (project) will be successful and live. So keep saving your pennies and get with someone that knows and work with a plan, all else will fail.
