I do believe it is stock length. and in the listing he said he had them sent out to be rebuilt.

 

Is your stock shock/swingarm still functional? If so, it is going to be even cheaper to just get the stock revalved/sprung now. It will certainly be a heck of a lot less setup hassle. I now have 2 stock YFZ rear shocks set up by GT Thunder. Both were good to go right out of the box with just a little ride height adjustment needed.

 

What do I have to do to make the no link setup work.

 

The rear shock would have to be sent out. It would need to have the appropriate valves and spring or springs for your weight and the swing arm set up.
Aftermarket swingers and links do strange things to shocks. Some xc links require that the rear shock be sent out otherwise you will bottom out hard with minimal effort.
This is not area of the ex that I know in depth. So this should be taken as general info not specific to a no link set up.

 

Exactly this. If you are close in weight and ride with the same intensity over similar terrain with the same size/weight tires as the last guy, that could be a put on and play part. That is assuming he had it set up correctly in the first place. Since it has just been rebuilt, possibly just a new spring for your weight. The fact that it says in the ad buyer must be committed to get the chassis set up and it can not be bolted to the stock location makes me think this will cost more time and money in the long run than it is worth. Pretty clear the seller believes the stock upper shock mount location is inadequate for this setup.