1970 Dart big block engine swap.

That is a red flag right there. If the Dana 60 has disc brakes on it then you need to match the front brakes to it or else you'll have a mess. Don't assume that you can mix and match random brake parts together and have something that works. You can't mix and match random brake parts anymore than you can mix and match random engine parts. Everything has to work together as a system.
Good info, thanks!