The BBK Kit puts the M-90 off to the passanger side. Makeing a dedicated lower, not necessary. However, they have stoped making this kit. Also I have seen people use the Kenne bell intakes.
www.kennebell.net You use either a stock or a GT-40 lower and the KB upper with the M-90 attached. Call KB to see what pricing would be just fot their intake. I have never seen a dedicated lower for a top mounted roots supercharger.(unless you could adapt a carb. one to fit a m-90) Both of the ways shown here are not intercolled.