Maybe I should ask.....Can ANY good machine shop do the work on the heads, or does it take some special type of Porsche knowledge to work on these heads? Is head work, head work, no matter the car?
Any head shop can do the job. The problem is, which toolmaker within the shop will do the job.
I had an experience with my Ducai 900 1980. I dropped the goods off, spent 1/2 hr telling the man at the desk how I wanted it done. Drove off and then remembered I had left my cheque book behind. (Was a while ago) Drove back and saw the machinist looking at my head and doing just what I didn't want done. I complained and he gave me my goods back and told me to f... off.
Went home and bought a milling machine. The rest is history as I run a machine shop now.
So the bottom line is, can you trust the person who is doing the job, not necessarly the company. References from others is probably the best way.