Very nice job!
But honestly two blowers are not going to be drivable more than a few miles because of the amount of heat each blower is generating. Its going to make great power because of boost but the air intake temp is going to be sky high, especially with one carb on each blower, less fuel to cool each blower. I have been thinking about building a similar set up except with a 6-71 on the engine and two 4-71's side by side on top. It will function just not very street friendly im sure.
Very nice job thou and thats just my 2 cents, let us know how it does!