"It is important to know because the manual calls for piston #1 to be TDC when adjusting the injection pump."
#1 is the flywheel side of the engine. Are you removing the injector pump
? If so make sure you remove the access cover (where the water
pump is) and spin the engine until the timing mark on the injector pump gear
AND on the drive gear line up. If you have lousy access to the rear of the engine (my Sabre's is tough) get a $99 bore scope
from Home Depot. It makes this dramatically easier to see. There is a 2:1 ratio between the pulleys so you might need to spin it over twice to get the marks to line up.
Removing the exhaust
riser (and manifold) really helped give more access to this area. On my MD7A I had a couple of corroded bolts due to a leaking water
pump. I had to drill them and that was not fun.
I initially tried to duplicate the injector timing based on where the old pump was. However, I found adjusting the timing based on the actual running of the engine seemed to work better. I would adjust it slightly, start engine and see how easily it started and how much smoke it had. I adjusted timing for the least amount of smoke and the engine has run great after that. Small movements make pretty big difference in the amount of gray smoke you get and also in how easily the engine starts. If the timing is off too much the engine won't start at all.