[WSSix]

It's like Todd said, the LS does it more reliably. Even with your goal of 700whp, the LS will be more reliable though it's arguable what constitute reliable at that power level. If you were wanting a lower power level, say 500 or so at the wheels, I'd say stay SBC because with a blower that's not difficult or really even pushing limits and a good EFI system will allow for good drivability.

The other thing to keep in mind when building a forced induction car is where the power comes on. As an example, to me, a Procharger is a terrible choice for a pro-touring car or really any car not being drag raced. Go drive one and you should realize very quickly that it does not produce a linear power band and they have terrible lag(I know nothing about their new intelligent design so maybe that's changed) which is not enjoyable when going on and off throttle and around corners. So achieving your goals with boost and how much boost will be needed also has to be taken into consideration. At 700whp, the LS will do this better as well needing less boost which will allow for an engine that isn't piss poor when not under boost.

I would recommend building towards the ultimate goal from the get go or else you'll be redoing lots of stuff. If going for 700whp is required to you, get an LS now and call that part done.