Using a 10 bolt diff. from a 67 nova, I ran a 15x10 with 5" bs rally wheel on the back of my 69. It has been a while since I owned the car, but it I remember correctly the early nova diff. was 4" narrower. I built my own tubs and ended up with 1.5" clearance on each side of the 295/50/15. The car sat low and the wheels tucked pretty good. If my memory is correct, you will be looking for a 15x10 with 7" bs after installing the dse mini tubs. Please don't take my word for it and measure before you order!
Also,
What rear suspension are you running?
What wheel are you looking to run?
Hope this helps so far.
David