Mine has a notch on the motor side of the damper (really small and hard/impossible to see). With a new to me XJ, I usually, use a small T square, mark the outside (front) of the damper and notch it with a cold chisel.
I´ve got a related guestion, is the index ("0") notch on the timing scale, the last notch or the next to last notch? I´ve read both, in various manuals.
The only time I use the timing marks, is for removal/replacement of the distributor and/or initial set-up of the motor.
Like 5-90 mentioned, there is really no iginition timing that can be set. Just initial set-up and sometimes after market cams (distributor gear varaiations) need to be delt with. Changing the position of the distributor, doesn´t change timing, but can affect the cam position sensor in the distributor (which also has a broad operating range).
If you have what appears to be timing issues, it is often a faulty sensor. Sometimes worn distributor gears or timing chain. The distributor in my 88 has an amazing amount of play in the gears and also the shaft moves up and down a rather large amount. Soon to be replaced with a tighter distributor and possibly a new timing chain.