I think that, if you are going to turbocharge it, at a bare minimum you should install a good quality set of head studs and replace the headgasket. And of course the EGT gauge before the turbine inlet. The studs and gasket are to help ensure that you don't blow the latter; with as long as that engine is, it's going to have a little harder time sealing than a tiny little four cylinder. From what I understand, sealing problems are somewhat characteristic of most inline six diesels.
Look into the differences between the 700 series turbodiesels and the 200 series NA diesels; Volkswagen/Volvo apparently did a good job with their changes to allow it to run a turbo, as the 700 TDs are from what I understand quite a reliable car.