From a DIYer's perspective, it is a huge job. Especially the first time. Pulling the head requires that the intake manifold come off which requires removing most of the injection plumbing. Getting the exhaust manifold off is no fun.
You will also need several hundred dollars worth of tools, including a slide rail pin puller and extended hex-bit sockets.
With that said, if you take your time, and are careful to follow the instructions, and check and double-check all of the alignments of the crank and cams, it will be a very satisfying repair. You will certainly learn a lot about your M116!
I hate to say it, but unless you are going to keep this car for a long time, you might consider just replacing the chain, cam gears and the upper rails.
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe