Sorry, can't agree with this at all.
If you were to set the mechanical advance distributor to fire 25 deg BTDC @ 1400 RPM, you'd have 5-10 degrees too much advance in the higher RPM range. How much load do you put on your M10 @ 1400 RPM vs 3000+? What power band are you operating in?
Just look at the advance specs shown in the shop manual, the standard (carb) distributor provides less total advance (with a different curve) than the tii/ti mechanical advance unit, that's one reason it has to be set with more advance earlier.
I'd suggest setting timing with consideration of the distributor's advance characteristics, with more emphasis on where the total advance ends up.
Not knowing off hand the specs of a mech adv. 002 dizzy would you recommend timing it closer to the 2400 tii spec?