I think a twin turbo with the supercharger would be a cool project.Now to answer your v8 question there is no replacement for displacement.With a v8 because of those extra 2 cylinders you get more torque at a lower rpm because of the greater rotating mass without having to use forced induction.This is why many times v8's and even some big straight 6's you get more torque than hp and peak is at a lower rpm.Look at some of these blown 4's that will have near 300hp for example but they have 25 to 20 lbs less torque where a v8 with say 300 hp will usually have 25-30 lbs more torque than hp.Others on this forum I'm sure know a lot more than me regarding forced induction but the issue I see in the twin turbo idea is you are going to be forcing pressurized air thru 2 intercoolers then to the throttle body which in turn goes thru the s/c increasing the boost again so even with a stock s/c and mild turbo boost you would be easily in the 30+psi range.More air means more fuel so you are going to need to get enough fuel delivered and most importantly the engine itself heads,valves etc are going to need to take that much pressure or kaflooey.