There was a proceedure for keeping the timing chain from dropping into the engine during cylinder head removal outlined in early Mercedes factory service manuals. After all the cylinder head bolts are removed remove the camshaft sprocket and have someone hold it up above the head to keep tension on the chain. You might get away with just removing the tensioner. Then lift the head slightly in the front and slip a stiff wire like an 1/8" welding rod beneath the head, passing through both sides of the timing chain just above the block surface. Now you can remove the sprocket and let the chain rest on top of the block. Align the engine at TDC first.