As one who HAS gone through this process before, I'd like to add some things here.
1) It is unlikely you will be able to spend "hours" on the phone with any one restorer. If they are on the phone they are not restoring and time is money.
2) It is helpful but not necessary to have the car close enough to you that you can check up on it now and then. Pictures are great but sometimes you need to see the car in the metal. I took about 4 trips during the process but should have taken a few more.
3) Every restorer has a style and "MO". Make sure they fit with your needs. Some will welcome your input, others won't. Remember the old sign? "LABOR RATE $45 hour; $55 hour if you watch; $65 hour if you help" I saved a lot of money by helping--not by working side by side of course, but by off-loading a lot of the "details" of restoration, such as taking care of sub-assemblies, sourcing parts, etc.
4) Some restorers operate like lawyers; you give them a retainer (X thousand dollars per month) and you have to keep giving them money. Is that what you want?
5) Check references AND work. My references were dead-nuts accurate in their description. The work I saw my restorer do, despite the awful backdrop, was excellent.
6) Some restorers are "over the top". One of them provided me with a description of the work done on a 113 which included half a page regarding all the meticulous detail required in "restoring" the starter motor, ending up with about 4 hours of labor. I decided that on sub assemblies like this, a factory rebuilt Bosch starter for $175 is the way to go. What would you do? Pay for restoration of a sub assembly or get a factory rebuilt on exchange?
7) Names are meaningless. Everyone's heard of Hatch & Sons, and Paul Russel & Company, most have heard of SL-Tech and Bud's Benz, but very few people have heard of Dave Payne, or Precious Metal, which was my restorer. His dark and dingy shop was in a derelict and scary run down neighborhood of Grand Rapids Michigan. The building was in need of paint--20 years ago. The paint booth appeared to be the finest in 1950's technology. But the work that came out of the shop was very very good, and very very reasonable even 5 years ago. I discovered him in a google search of Mercedes Parts, which led to K&K Manufacturing, which had a link to Precious Metal (since gone, I'm afraid) You might find many shops that are similar. It is all in the hands and eyes of the "director" or restorer.
Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored