Need disc brake help!

Need a lot more info- "a kit from marketplace" doesn't give us much to go on.
Is it a factory or factory based setup? Kelsey-Hayes (4" bolt circle, 4 piston), later A body (single piston, 4 1/2" bolt circle), F/M/J body (similar to A, taller spindle), a Scarebird type kit with a potpourri of different parts, or even a Wilwood, Baer or other proprietary style kit?
Calipers to the rear is commonly done to provide sway bar clearance.