Nothing wrong with having tubular manifolds.
If you're looking for 700whp, build the engine with 10:1 and use a pair of 68mm turbos, with .68 a/r housings. If you're doing a single, an 80mm would be just right.
These two suggestions will make over 700hp with supporting mods, but I'm considering the higher compression 6.0L.
They will spool up just fine and have room for future upgrades.

The owner can chime in if he wants, but one of the best stroker engines (408) I've had experience with was a 10.6:1 408 we built.
It had great NA power, boost came in just fine, almost too fast with .68's, and easily made over 830hp on low boost, on pump gas.
With more pressure and race gas, I bet it would be a 1000whp engine.