I'm in the process of doing the same thing but I'm using the bolts from the donor kit. But not exactly sure what your asking. Mine for the 69 Dart came from a 73 Duster. Perhaps a picture to see what you're doing?
Bolts that attach the spindle to lower ball joint are much too large a diameter to fit the stock lower ball joint. These bolts came with the kit/parts I purchased, I did not receive a new lower ball joint. So my assumption is the lower ball joint that works with this new spindle must be an upgrade or different than stock.
