Here is how I re-installed my rear door check.
This is a 1970 Series IIA. The rear door had an aluminum chequerplate sheet over it , so I had no access to the original channel for the door check rod. That channel is not available as a part and is integrated into the door frame.
I bought a new rod, and then figured out that I could buy a ready made channel for it buy getting one that is made for the Defender. It fit perfectly!
I bolted it on using a hex head bolt, lockwasher and nut on the closest hole because there was already a hole through the door for this (holding on the aluminum chequerplate).
I used hex-head sheet metal screws for the other attaching points because I did not want to drill all the way through the door in order to use bolts. The stress on the channel is sideways, so I feel that the sheet metal screws are sufficient.