Hello Gorthaur,
we have some well known and experienced independent Porsche shops over here in the Stuttgart area with guys that have formerly worked at Porsche.
But it think it's not worth to do such a long travel for just changing a clutch and an ISMB. Also it's not rocket science to do that if you have the right tools and some experience in Porsche water cooled cars and if the mechanic does his job meticulous. OK, maybe Jake will say it's rocket science.
That's OK.
Regards from Germany,
Markus