Yes, they have "taken apart" a zillion heads, but that means REMOVING VALVES, SPRINGS, KEEPERS AND RETAINERS, then grinding the valves, seats and putting those parts back together. I have never seen a shop where they are anxious to do any of the other parts.
Disassembling, assembling these parts on a bench is a pain because the head wants to scoot around. On the engine it is tied solidly in place.
There are many really good machine shops that do valve jobs on Chevies, Fords, Toyotas and who knows what all day long, but rarely see a M103 head. If you don't know to tighten all the cam journals down gradually and tighten one before the others you will strip the soft aluminum bolt holes in the head, and you can even break a camshaft. Many machinists would NOT know this. Again, they are machinists, they grind valves and seats for a living, they don't do mechanical work. THAT IS NOT THEIR EXPERTISE. I have one of the best machinists in Texas and trust him to the "inth" degree with machine work, but I'll do the mechanical work to know that it's done right, thank you very much.
THERE IS ONE MORE IMPORTANT REASON FOR REMOVING AND REPLACING THE CAM WITH HEAD IN PLACE!!!!!!!!!!!!!!!!! If the cam is in place, some of the valves will be open and subject to damage while putting the head into proper position. With the cam OUT of the head, all valves are closed. Additionally if you carelessly try to turn the engine while the head is in place to time the camshaft, you can bend valves.
I suppose everyone just thinks I talk to hear my head rattle. There are REASONS for doing things a particular way!
Have a great day,