[Kraftwerk]

I would do the following:
Rebuild the engine first, tune everything to stock specifications, except for ported head...port it as much as you can, keeping it safe...since the biggest problem about theese engnes is the head - they're not crossfow, valves are tiny, valve lift isn't much either, etc...focus on that first.

Then, turbocharger:
I would go to about 20psi, just block off the wastegate or put an eBay (or even DIY, it's simple) manual boost controller (MBC), install a eBay (or sourced from a wrecker) intercooler, fit pyrometer and turbo boost gauge as a precaution and keep a close eye on it.
Further, IP pump unleashed...take the governor out, block the main spring with 2-3 shims, set the fueling screw accordingly, up the low pressure fuelling, do turn the fuel pin or even grind it (but I don't think you will really need that) and you should be all set.
I'm preparing (actually, gathering informations and waiting for more free time on hand) to do it myself on my wagon...looking for something over 300Nm, don't really have an idea on horsepower...but might be fun.