At 6-1/2 or 8 psi, for starters, I'm pretty sure the stock internals could handle it. Anything above that, and you'd have to get creative with charge-coolers, and possibly reduced compression ratios (which will make it less powerful than stock, until the turbo spools up).
I'd use a pair of relatively small turbos, for quicker response, and set it up for port-fuel injection, possibly with the Weber-pattern throttle bodies. Combining the engine management (fuel + ignition) with the aid of inlet temperature & exhaust gas monitoring (wideband O2 sensors) plus 1 or 2 knock sensor inputs, and you'd have a fairly efficient setup...
Or, you could swap in a BMW 3.0 N-54 (or even an N-55, like my wife's X5 has) stand it upright, and have >300bhp/>300Lb-ft with a lot less experimenting. But what would be the fun in that?!?!