NEED Help drum to disk conversion

I switched from drums to disc on my 1964 Valiant. I took disc setup from a 1975 Duster. I had to use the upper control arm from the 1975 Duster, but retained the lower control arm from the 1964 Valiant. This I beleive, is because of the different size balljoint for the disc spindle on the upper control arm. Mike