To get everything to line up, the chain needs to have its slack on the right side where it would be taken up by the tensioner if the engine was running. It needs to be tight between the right and left sprockets.
If you have everything positioned like this and you are still off, then try repositioning the sprockets to get the marks to line up. Turn the engine over a couple of turn by hand to verify that you are not having any piston-valve contact.
Then crank the engine for a few seconds with the coil wire unplugged. You should build up oil pressure in the tensioner, and the chain will tighten. Do one final check of the cam marks - you should be dead/spot/right on at TDC and good to go.
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