What do I need to do to build a 1000hp turbo small block

dusterdoug said
Mopar R3 block if you can find one. Or a new Ritter block. $3000+ and the machine shop bill afterwards. OE block "might" take 1000 HP...at least once before the ka-boom.

At your proposed power level, go Gen 3 Hemi and don't look back. Many G3 OE blocks can take that abuse and survive.

This comment is the best so far. You’re standard LA and Magnum engines won’t take you anywhere near 1000 hp. Build a gen 3 hemi and even then you will still need deep pockets.