Using mustang rotors for 4.5" bc

I didn't take any pics, here's a diagram of what happened. the seal wound up riding about .040 out (towards the spindle nut) than origional, which is fine. The seat depth is the most critical cut. I first tried to have the machinist match the stock rotor, that didn't go very well. Then I installed just the outer bearing, washer and nut and bottomed it out, measured from the end of the spindle to the nut. Then installed the new rotor and had them cut the difference, minus about .010 so the bearing wouldn't bottom. That's why I don't have a solid number on how much to cut.
Find a meticulous machinist, mine was used to working on tractor parts I think.

That`s exactly what I was referring to, each mod seems to be just a little different. I appreciate the input.

I can't wait to try this mod.. I have a set of KH spindles, dust shields, calipers.. will these work on my 68 dart that came equiped with drum brakes?

Yes, once you`ve installed the disc brake spindles, you can then incorporate the machined Mustang rotors and the original calipers.