Look at it this way.
ZZP's base Z3 kit on a GT (for around two grand or less if you can find stuff used...which is the way to go IMO) with the addition of some crap EBay intercooler and piping you can fab up yourself for cheap = 350+ WHP when running over 12~ psi I'd imagine.
Also, only thing about that is you have to remove the downpipe, tuck some harness' away from the turbo, and other small crap.
No head removal.
No balancer removal.
Everything stays on, as do the fluids...well minus the oil change because you have to run a feed line from the pan level sensor.
I'd venture to say it is quiet easier to do than a top swap IMO.
I've done a couple Top Swaps...they aren't fun. I'd rather pull the motor than do that crap in the car.