5.60s is not a problem, you could do that with a 40 shot and arm extensions.
A Garrett (or Turbonetics, or Precision) 50 trim TO4E / T3 stage 3 turbine is a popular, tough, and relatively cheap turbo that will spool quickly and still be able to make 400hp. You can find one online for $600.
If he wants a street/strip turbo, a Garrett GT28R ball bearing is a good choice. Little pricier, limited to maybe 325hp, but will spool a little quicker.
But if it's just drag, stick with a journal bearing T3/T4 hybrid. The ball bearing turbos are more touchy, and the center sections can't be rebuilt. If you hurt it, it's done.