I've seen a couple of books listed on vendor sites about doing what
you want to do. The 289, with some minor changes, is the engine Shelby
used for racing which blew away the competition. And there's much more
you can do to it. Like a Paxton supercharger Novi 1200 maybe.  Change
the points to elctronic, hotter coil, better plug wires. :0) 347 kit?

In addition to books mentioned, some of the articles in Mustang
Monthly, Mustang and Fords, etc, list what was done to the cars
depicted.  Also, there have been articles which dealt specifically
with building up the 289. You might try their tech pages or back
issues.