The Cab looks clean, I can see how it caught your eye.
I prefer the supercharger to the turbo set-up. What makes these M engines to me is the daily drivability, but when you get into it, the power is there. The blower keeps that driveability, but when you get into it, you smile... Come spring, I'll take you for a spin.
Because the power is further up the rev range, you can run more boost safely. 12 lbs boost on my car is at higher RPM's, so you're not stressing the stock internals at 3000
rpm's. 8+ lbs on a turbo, you'll need some top end work.
The numbers you quoted you can do with a blower without aftercooling. I was running s unique DINAN set-up before the AA tune and was about 360 crank.
The S54 is a high strung motor and not the easiest to work on.
Find out some history on the cab. Where it was serviced, etc...
Now for the supercharger....