You’ll be hunting forever. They didn’t make one. 4 7/8 back space was the most on an 8.5 Centerline. These will have your tire within a millimeter or two of touching the springs..
It’s the tire bulge or section width that you need to worry about.
With 15x8 rims with 4.5 backspacing at 245/50/15 tires I had no touching to leaf springs or inner wheel well. It was close though. That's "stock" small bolt A-body rear width with stock axle flanges and drum brakes (just re-drilled bolt pattern). OE Leaf springs 100% stock location. That’s the inside clearance.
67-69 barracuda have more outside clearance than 67-69 Darts. So that’s not comparable.
The low profile tires without much budge or flex help a ton.