15" steel rims for (4") small bolt pattern?

Trying to get 15" factory steelies on the rear of my (small bolt pattern)
68 dart, i know 15's never came in the 4" bolt pattern.

I was hoping Stockton Wheels in California could do custom small bolt pattern, 15" rim?

Would it be safe to order a 7" wide rim?
What about the backspace for a 68 dart?

I was thinking it would be a 4" backspace but my rear end is out now so i can't measure.

Thanks very much for any input