Well that should be easy, those are exactly what we're talking about. 10" drums, 5x4" pattern, should be large ball joint.
All you have to do is clean up the upper ball joint and measure it across the flats, should be ~1.9". The ball joint stud at the top of the taper should be ~.724". And measure the bolt pattern, should be 5x4".
For whatever it is worth here are some pics. This set up was on my 71 Demon and my 67 Dart. Obviously upgraded at one point. Both 4.5 with big upper joints and 10 inch drums.