Moser Rear to Narrow or not to Narrow?

For the 68 Dart project we are Purchasing a Moser Dana 60 w. disc brakes. Mini Tub and spring relocation in progress, springs are CalTracs.

1. We will run DOT slicks so want the largest we can get in the space, is it possable to get 12" tire in this space?
2. Before I order the Dana 60 should I have it narrowed from the stock width to get it centered in the wheel well opening or leave it stock width and move wheel inboard using specific backspace?
3. Also what combos tire & wheel are popular for this setup I am trying to get?
Thanx