The 3 point dimensions were changed along the way but I can not say with certainty when.
As you know I am much more familiar with the Thousands.
A couple of things that make me think thus:
1)I had a Dearborn/Danuser 19-16 back blade. It worked normally on the 2N/8Ns I had. When I tried to put it on a 3000 it did not work correctly and the whole 3 pt kind of layed down flat. (don't know how better to describe it) I tried it on a 641 and it was the same as the 3000. 2) I also had a Dearborn 22-XX cordwood saw that I restored and used it on the back of an N. Worked good. Lift it to transport position and the belt would loosen and saw would stop.
Put it on the 3000 and the belt would not loosen in transport position - blade kept spinning.
Tried it on a 641 and same problem.
3) Had a Dearborn/Danuser post hole digger and on the 3000 it would barely lift high enough for the auger to clear the ground in up position. Same with the 641. Never tried that on an N.
4) If you buy a set of aftermarket under axle brackets like in the photo you have to use the correct hole or else the stab bars will bind. They fit fine on the fender bolts on all Ns, Hundreds and Thousands. But the hole that lines up with the lower lift pin is different. I don't remember exactly which is which but I think the rearmost hole fits the hundreds/thousands and the center hole fits the Ns. Might be vice versa.
I have asked this question about the change in geometry before - both here and on the Ford board but never got an answer. Most people didn't know what I was talking about.
I don't know how/when things changed and only assumed in was with the Hundreds.
As for using a Dearborn sickle mower on your dad's 600 I wonder if the different models 14-13,14-14,15-15,14-16 had something to do with the geometry. But could be blade length or something else too. Likewise there were several 22-XX cordwood saws which looked identical but may have been for N/NAA vs 100/1000.
I've had most of a dozen different dearborn/ford plows over the years and they worked on both Ns and thousands.
I think the changes are the length of the lift arms and the height between the lower lift pins and the top link may be different.
Likewise I'm pretty sure the original Ford/Dearborn stab/underaxle brackets for an N will not work correctly on a Hundred.
No one ever showed much interest in these differences so I've never pursued it.
Sorry so long...