Few comments, first of all you have A LOT of room to work with packaging 6 turbos in, let alone 2, let alone 1. Nothing to worry about there...

I wouldn't worry about the block at all. 1200hp is sort of a joke. Honestly it would be a waste of a motor that good. You could make 1200hp with a 383/400 and Indy SR heads. WAAAAAY cheaper, and WAAAAY easier.

As trendz said, EFI is nice, amazing drivability, and tuning to the greatest degree. But no one can argue with the fact that you can simply bolt a carb on and go... no tuning needed other then the occasional jet change.