[Woodz428]

You have several options, if you indeed have 6 cyl spindles. All drum brake spindles until they went to Discs, used 4 bolts to hold the brake backing plate on, They are the same bolt pattern. You could find some early ones, I believe until '67, that use the same balljoint and tie rod ends or '68 and later and swap to the heavier tie rod ends. I believe Mustangs Plus offers the adapter parts to swap the later spindles on to the early car.
If you decide to go that way, I have several sets of late model drum brake spindles.
In addition, those spindles are also the same as a Falcon of the era, that's what they made the Mustang from, so most chassis pieces are the same.