When I built my 351w I bought the BDS intake. Sucks that us ford guys have to spend that much, I think I spent 750$ for mine. Anyhow its base is a Dual 4bbl manifold by offenhouser with the top cut off. Hamptons has one also, but if I remember its the same price. The BDS is a the way to go, its just high enough you dont have to buy a special distributor for the motor.
I tried to buy those plates with the idea I would weld my own intake, and the blower people want to keep thier monopoly, they wouldnt sell me the adapter only.
By the way wait until you want to mount your lower pulley and BDS wants 450$ for the harmonic balancer. Not only expensive but its an anchor!!!..., its a huge o'l heavy thing, I would of never used it had I known it was so heavy.
Ben