I went through this fire drill on one of my 4T's, and never forgot what I did, as I was stumped for a bit over it.
#1 piston (one closest to the radiator, the book fails to ID which is #1)top dead center or leading up to that, put a cork in the spark plug hole, it will pop out or you can feel air with your hand, at the same time that timing mark on the starting engine flywheel is coming up to line up with the mark on the case. The motor is now ready to fire and is in time, all you have to do is make sure that mag is hot, and will fire that plug wire at this time, you want the mag to be leading up to snapping over to fire the spark on the #1 cylinder and be able to mount it with the coupler lined up with the slot, ( I had trouble with this myself). I can recall firing that mag in my handm snapping it over to make sure it went #1 then #2, don't recall it skipping then firing #2, I think each time it snaps over, it fires a spark. Once I had that sequence lined up and could install it to line up with the motor, and the motor was ready to fire #1, that was it. As far as advance and adjustments to the mag, can't comment there, but if the mag is working properly, it ought to fire that spark at the right time.
Use care with the starting motor, keep the oil clean, drain or run out the carb each time, preventing any leakdown, shut off the valve on the sediment bowl, be ready to grab the governor linkage in case of an overspeed when the diesel fires, you may already know these things, and also make sure the diesel is spinning if the starting engine is running, so it gets coolant circulated through it.