Sorry to join the party so late. As for intercoolers, they are alway a good idea on any turbo setup. (Well, with the exception of a draw through as the fuel will puddle in the bottom and make a nice pressurized bomb, but I digress already.) The nature of gasses when compressed is that the temperature rises. Anything that takes heat out of the intake helps in the prevention of detonation.
I guess I'll have to concede that that does include water injection but I still don't think I totally approve of that. I mean, why waste that valuable space with uncombustable steam when you could put in more air and fuel? Yes it works, but so does a real intercooler and you won't run out of that.
Blow off valves are necessary on a blow through because when you lift of the throttle under boost, the pressure on the top of the float bowl is still high but the idle jet outlets under the throttles are in vacuum. This leads to a "pig rich" situation every time you go to shift. Of course there is the added benefit that the turbo doesn't get hit with a return pressure wave and doesn't take as long to build boost again. Win win situation.
On the other hand, blow off valves are phenomenally bad ideas on draw through systems. Think about it.
For these two reasons, one should abandon the thought of a draw through system, in my opinion.
(Oops, I just thought about it. You wouldn't need a blow off valve on a draw through since there is never a time when the boost side sees a restriction like a closed throttle. Still, draw through is not the way to go.)
As for using the SUs in a blow through system, I don't know what they would do. My initial reaction is they won't work but I have not thought it through enough to give a valid reason.
In the "Box the Carb" vs "Plenum on the inlet" argument, I lean toward boxing the whole carb. That way, all of the passages and gaskets and shafts and such "see" pressure as if the altitude had changed.
With the plenum, there is the potential for the throttle shafts to spew fuel/air mixture or the float bowl gasket to blow out or those little lead plugs to pop out sending streams of fuel onto a hot engine.
Well, that's about all I have to say.