I learned the hard way, make sure the flange of the injector pump and the timing chain cover have a matching mark so timing can be matched again easily when re-installed.
My old tractor 1974 MF135 has slots to adjust the timing. Newer ones just have holes and I guess they don't adjust as much.
I found a Lucas CAV book online as A download, but it was several years ago.
If I can find it I will post a link.
What year are we talking about?