If you've done one benz valve job, you can do it again. If you've never done one, now probably isn't the time to learn.
The alloy engines have several gotchas, including threads in the block stripping out.
You can probably find a used engine w/o too much trouble. Once you find it, go ahead and try and fix this one if you have the time & money to practice.
You're looking at upwards to 900$ for parts+machine work on just a valve job. That includes new guides, gaskets, getting the various fasteners cleaned and etched (or just replacing them), all the rubber hoses. You'll spend more if you decide to rering the engine, since "you'll be in the neighborhood".
There are several execellent sources of parts mail order for the job, http://www.epsparts.com/
& firstname.lastname@example.org & email@example.com are my favorites.
Be prepared to pick up about 140$ worth of specialized tools for the job. There are two specialized allen key sockets to remove and install the head. There is a specialized tool to remove the metal pins that hold in the timing chain rails. These are unique to the mercedes benz.
Lastly, don't forget to budget time. It takes me a weekend to tear apart a motor for a valve job. My machinist takes the better part of a week to get around to telling me what size guides he wants and then the following week is spent getting the work done (he's a busy guy. He handles all the machine work for several Long Island dealerships). Finally, another weekend is spent reassembling everything.
Last time, a 3rd weekend was spent finishing up the reassembly and getting the car to run just right. It was a 73 350slc that I bought in the state you're talking about. It was a rust bucket and the engine was blown. It's now a happy engine sitting in my garage, waiting for transplant into a 250se/c. The body was parted out as soon as I was sure the engine was back in one piece.