a 400 with 9.5:1 or so compression pistons (like kb240's) and alum heads will walk that 5.9 magnum like a dog. even without a stroker kit ( the real expensive one with a set of kb215 pistons and 440 forged crank lol)
he should get both engines and build the 400 for a later upgrade
in case you dont believe me... here's a guy with a 383 doing a 9.8 second pass in a 3100 pound car:
[ame="http://www.youtube.com/watch?v=9K6ard18yo8"]http://www.youtube.com/watch?v=9K6ard18yo8[/ame]