2JZ is a better choice if you have the room because the exhaust and intake are the same side as the 'slant' motor BMWs... ie exh on driver's side, intake on passenger.
Here's my old E30 with 2.8L built motor
My vote is keep it BMW, it's heaps cheaper to drop in a M20 2.8L inline 6 from E36 3 series (bottom end is the same, you get twin cam heads), then supercharge it with a kit or turbocharge it. If you've got $$ then E36 M3 motor and super/turbo it.
More from me in the morning when I can be bothered typing.