Ouch. That's a hefty load to assume so early in the ownership process.
My IP is going back later this week, so I've been heavily researching the process, myself. I have a W115 240D, so my numbers and specs might not apply, but perhaps my post can serve as a rough guideline.
To pull/install an IP on a 616 requires the crank to be set at 45 degrees below top dead center on the compression stroke.
Further, there are marks on the front of the IP. One is on the spline, itself (properly a gap of two teeth) and then a mark on the housing. When reinstalling, the cam needs to be set two teeth before delivery. That is, the gap on the splines needs to be two teeth counterclockwise from the mark on the housing. With the 616, the IP will "rachet" two spots when reattached to the block and and the timing should then be on.
Here's a blurry photo that I happen to have on my phone. Hopefully you can see the mark on the housing and line it up with the splines to get an idea of what I'm talking about. The line on the housing is faint, but you can see it at roughly the 12 o'clock position just above the splines.
As for the coupling, even though there's a key way I don't think it matters how you line it up since there's no key.
Once it's loosely bolted back in place, and fuel lines reconnected, you'll need to dial in the timing. That's an entirely different thread.
If it were me and I had my IP out and I planned on having the car for a while, I'd have it bench tested. It cost about $300 for my local Bosch shop to test mine, and another $450 or so to replace and repair the worn and broken parts.