Welcome, from one 351W P72 owner to another!
The biggest things the 351 cars lack is axle ratio and carburetion.
Your rear axle almost certainly has a 2.73:1 ratio ring and pinion set, and while that's good for highway fuel economy, it doesn't help for much of anything else. I personally switched to a 3.55:1 axle ratio and have been very happy with it. It gives plenty of reduction for off-the-line acceleration, but isn't so much that the engine is spinning insanely fast on the highway and ruining fuel economy. Just remember that whatever ratio you choose should be matched to the engine's powerband.
As for the carburetion, your car is equipped with the Motorcraft Variable Venturi carburetor. It's one of the most maligned carburetors in automotive history, although mine has behaved fairly well, so I'm not convinced it's as poor a design as everyone says. That said, however, it IS too small for the engine. It only flows around 350 cfm, and your engine, depending on what else you do to it, could use more along the lines of 500-700 cfm. If you want a simple build that'll give you decent power, I'd suggest a dual plane 4 barrel intake (Edelbrock or the like) and an Edelbrock 1406 carburetor. That will make the engine much more happy on the intake side.
There are other restrictions as well, of course, exhaust being another major one, along with cylinder head port design, valve size, and camshaft profile. That said, just changing axle ratio and carburetion should make a very noticeable difference. Feel free to ask more questions, and also, check out Grandmarq.net
. It's a forum that I'm a member of, and which has more expertise on the "box" style cars than this one does.