B Body rear end in a 71 demon

I don't know who is building the new "centerlines", so I don't know what their backspace is.
The original Centerline Tool autodrags were available in 15x8 1/2 with two backspaces, 3 5/16, and 4 7/8. The 4 7/8 will certainly work best for you.
The 17" mustangs should also work, but might have too much backspace. That is easily fixed with wheel spacers. I would look for 5-5 1/2 bs. Late mopars won't work, bolt pattern is different.
New mustang wheels are available anywhere, eBay for used mustangs or centerlines. Google can be your freind.