Backspacing?

[renegade8720]

Hi, I need advice from the Lords of knowledge. I am getting ready to order my wheels for my 1950 3100 truck.
I will be using 15" wheels. I am building a pro tour, and will be using 15 x 14 with 4" to 5" backspacing in the rear bolted to a narrowed 9" rearend.
I will be installing a mustang II front end with stock height spindles. I want to use 15 x 7 wheels and want to know what backspacing will work with this front end set up. I don't want any fit or rub issues when turning.
Please give some advise on what backspacing will work.

Thanks for your help,

Renegade