Life is not that simple.
That is not the only harness you need to replace. You will also find the wires that go from the coils to the power on the drivers side are bad too and should be replaced at the same time.
The Mercedes harness will save you many hours of work so do not discount just buying the harness. I know you have lots of time and no money. Still the value is there is getting something ready to go. This is from someone who could have wired his own from scratch, I paid for the full harness. If you not electrically proficient then you might not want to consider making your own harness, too many ways to mess up and you need to know enough to be able to check your work. If you do not own meter and do not know how to use one, then you may be much better off paying for the harness. They can be found cheaper if you look around. Dealers get them for closer to $500.
My brother has done many of these harnesses. When working with the original replacement parts you start by just cutting all the wires off at the terminals. Then you flop the new harness in place, bolt it down and start swapping the connectors. Some of the wires at the front of the engine have a specific routing and it is wise to follow that routing.
You must take the oil filter off and the throttle body. Be careful as the throttle body wires are bad too. For that matter assume all wires you touch are bad and you can make them worse. If someone had played a lot then you might find a lot more problems with bad wires that are hidden.
Some other hints.
The connector below the manifold is a PIA, no room. Expect to only get one screw back in place unless you are true glutton for punishment. You need to take the starter out to change the coil wires.
A lift make the job go MUCH faster. You will have the car go up and down several times. Working on your back will add hours to the job.
Pay attention to what your are doing. You can disturb other stuff that will only increase the time and cost of the job. If you do not plan on replacing a wire then do not disturb it. Assume all the wires are bad and can be made worse if you move them too much.
Since you do not know if it ran before you got it, you are not going to know what else is wrong.