I like the idea as the DOHC KA seems to be a very good performance motor platform, at least in paper. Should provide huge amounts of mid range torque in a responsive manner when supercharged well. If we had KA's in Europe, I wouldn't even look at an overpriced SR piece of shit with the worst valvetrain geometry in the history of DOHC cylinder heads and 4 desiliters less in displacement.
Do it properly though, and go for a twin screw supercharger [Lysholm, Whipple (if they do small enough) or 4th gen Eaton], or not at all. The efficiency of those units are superior to any other metod of forced induction, period.
A centrifugal charger will never be better than a poorly designed turbo system, as the compressor's nature is similar to a turbocharger's but won't ever be steady on the sweet efficiency islands like it would on a properly carried out turbo application.
A roots blower shouldn't even be an option unless you just want a little more power on mild boost, and even then the amount of work involved will be plenty compared to a turbo kit. The efficiency usually drops dramatically after 10psi or so, thus resulting in high intake temperatures, bad power outputs and a risk of detonation.