wheels for Disc Brake Conversion

Hello all,

How far does the disc brake conversion push the wheel out over 10" drum on a 74 Duster? I'm looking at getting a set of 61C(direct bolt) series Cragar SS using 205 60r15 T/A tires. The 15X6 wheels have a 3-1/4" backspace and the 15X7 have a 4" backspace. Summit recommended the 15X7 for future tire options. Do I need any special considerations for safety or room? Of the two which would you run?

v/r
Ron