6 cyl head has .016 warp, should I fix?
 

My machinist will only skim (machine) it flat if no more than .010 warp. He said he knows a specialist who will clamp and heat it flatter ($100) so that he can skim it completely flat.

The machinist said these heads were prone to warping because of their length.

Should I have the flattening done or find another used head that is flatter?

I'd want to keep the original head if the only thing wrong with it is that it's warped.
Not being a machinist, I don't know if what he is telling you is true, never had a machine shop tell me they couldn't machine the head though, and I've had a lot of them sent in. Would $100 be the total bill? Or just for the job the specialist will do, and you need to add in the price of planing?
Gilly

My 190E 2.3 (4 cylinder) was machined .020 by the shop I went to for the head refurb and I didn't have any problems.

I've had heads flattened by a competent shop and it worked well. With an OHC head, a warped head can move the cam bearings out of line. I've seen a few heads, Benz and others, ruined because of this. I remember one BMW head so warped I couldn't get the cam out of the head.

Straightening it is an $100 extra. It will still need machine skimming and the other machine work. I don't want to add costs if not necessary.

This one is actually a spare head same year & body. I thought I'd have it ready so when I removed the existing head I could go ahead and install this.

I can remove the existing head and trash this. I can also buy another used head at the PNP but used heads are a crap shoot as far as condition. It needs a rebuild because it either blew a gasket, leaks, or in my case is not allowing it to pass smog emissions.