OEM gearing on our Panteras is 4.22 to 1. 3.77 to 1 gearing widens the ratio between each gear a bit, allows each gear to wind a little further, allows you to reach 60 in first (which should give you that 4 second 0 to 60 you are looking for), gives you a somewhat more relaxed cruise speed and will allow the car to attain a top speed in the 170 mph neighborhood.
All of the Ford small block V8's are thin wall castings, therefore the 302 is lightest, the 351C is in the middle, the 351W is a bit heavier.
The 351W is taller than the Cleveland, but not by a great deal. I have never seen a 351W fit under the engine screen, because everybody runs the "spider" type, high rise intake manifolds (Edelbrock Victors or Ford Motorsport). My guess is that with a conventional, low rise 2 plane intake it would be possible to get the carb & air filter under the late model L engine screen. Jerry at PI Motorsports will have a better idea, since he is involved with the Viper Spanker motor swaps (427 cubic inch 351W).
The PI Viper Spanker may be a motor for you to consider. They rate it at 500 bhp.
From bellhousing flange to the water pump tip, the 351W & Cleveland are again about the same length.
Supercharging?! Isn't a naturally aspirated 500 bhp 427 windsor enough? I'm just kidding around.
There are other Pantera owners with experience supercharging the Pantera. I have none. I have seen B&M superchargers squeezed on top of the 351C. There are 2 pictures of one in Wallace Wyss' book, "DeTomaso, the Man and the Machines". Page 123 shows the routing of the belt drive from the passenger compartment, page 161 shows the clearance under the engine screen. Obvious from the pictures, a Holly carb sitting on top would have to poke through the engine screen, but a pair of side draft Webers might squeeze beneath the late model L screen. With a Windsor motor your selection for supercharging would include the products made by Kenne Bell for '89 - '96 model Mustangs designed to operate in conjunction with EEC IV fuel injection.
regards, George