HE351 and GT3582R are pretty close in terms of wheel diameters, for the record. The Holset has a larger compressor but the Garrett has a larger turbine.
Compressor
HE351CW: 86mm exducer
GT3582R: 82mm exducer
Turbine
HE351CW: 65mm inducer
GT3582R: 68mm inducer
Well, thats also considering he is using a genuine 3582...
but also goes to what I was saying. On a fairly stock motor arrangement, the 3582 will be a bit lazy. Especially if only 300-350whp is what is wanted.