Hope I did right

[WS6]

Those power levels are out of my range of knowledge honestly. I believe you will need to switch to the cast iron block though for peice of mind. I think the aluminum ones are only good to about 800 reliably. LS1tech will have the info you need on what the blocks can handle. Personally, I feel the added weight of the cast iron block is worth the durability at those levels. Besides you want be able to tell the difference from behind the driver's wheel.

If you choose to switch to the cast block, you can use the current engine for trial and error and getting any bugs/fitment issues sorted out. Save your money, build the other engine, and then just swap when your ready or you blow the aluminum one.