TorqStorm Ford 351 Windsor Supercharger Kits
TorqStorm makes a centrifugal supercharger system for 351Ws for $2800, but you'll have to buy a blow through carburetor. I believe TorqStorm will sell you a Quick Fuel blow through carburetor as additional equipment, but I don't know how much more that would add to your total cost. There's a contact number on their website, so you can call them for all the details.
A centrifugal supercharger won't provide as much low end torque as a roots-style supercharger, but the boost will (in general) kick in faster than with twin turbos.
Here's an interesting article comparing a Chevy 305 and a Ford 302, before and after adding a TorqStorm. The improvement in hp in both engines was staggering.
http://www.hotrod.com/articles/5-0l-...4-storm-rages/