I was thinking that I could pick out an object 75-100 yards out with my irons, leave the rifle in that position, then move the dot to the point just above the front sight post. Will this work?

With the red dot turned off, sight in your iron at 50 yards.  make sure your cheel weld is consistant, because the iron sight needs a fixed head position for repeated shots.

Once you sight in your iron, then turn on the red dot and move the red dot to the front sight post. zero check your weapon at 50 yards to see if everything lines up.  if the red dot is off a bit, adjust the red dot to zero.