I have a couple of N/A big blocks (580 and a 655). These are pretty much race engines but not total all out deals as we bracket race. They make great torque but I wouldn't class them as drive anywhere street engines. (cam lifts are .750" and .850"+ respectively)
I love the look of a roots blower, just something about them but a centrifugal style blower is a lot more efficient. No reason why a properly tuned one wouldn't work on a small block, I've toyed with the idea myself but the idea had major mission creep (as all idea's do) so we just concentrate on the N/A stuff.