When I was designing a layout measured the over-hang and "in-hang" of my larger engines. My measurements were all from the end of the ties from GarGaves and Ross track. And if I recall correctly the ties in both cases are 2 1/8" long. So on O-72 my MTH Big boy has an over-hang of 2" & in-hang oh 7/16 ".
Of course we all know that no two manufactures O-72 or any other size track are necessarily the same size "curve." Even garGrave vs Ross O-72 are slightly different.
Ron