lol, you mark it before you pull it out
I just had to do that earlier this week and it was a bitch to get back in. You have to have it back in on the right tooth otherwise your timing will be all to hell.
You'll have to put it in about where you think is right and see if it starts up. If not move it around a tooth or whatever and see if that works. I'm sure someone else will have a better method than that, but thats what I ended up doing. Actually, I got engine to TDC and lined up the arm inside the CAS with the trigger and put it in there. DIdn't work but it wasn't far out. Carefully removed it enough to turn it around one tooth and tried again. Took a while, but its all sweet now