backspace is the wrong way to talk about what you want your wheels to look like, so lets talk about FRONTspace instead.
first a little info:
backspace and wheel width mean a lot, offset and wheel width means even more. a 4" backspace 7 inch wheel will fit (very) differently than a 4" backspace 9 inch wheel. this is because of frontspace. same thing with different widths but having the same offset.
wheel width is measured bead to bead. a wheel is ~1" wider lip to lip than its stated width because of the lips. so a 7 inch wide wheel is 8 inches wide with a tape measure lip to lip. a 6 inch wheel is 7 inches wide. etc.
backspace is the measurement from the rear LIP to the axle mounting surface.
offset is the measurement from the wheel centerline to the axle mounting surface.
this is why I talked about the width lip to lip measurement, because backspace takes 1/2" of the lip into account. so the wheel you just described, 7 inches wide, 4 inch backspace, 0 offset. 0 offset indicates the axle mounting is exactly in the center of the wheel. a 7 inch wide wheel is 8 inches wide lip to lip, and 4 inches of backspace means the axle mounting surface is indeed in the exact center.
to run without spacers, I know that a 10 inch wide wheel with 4" backspace will fill up the rear fender, no spacers. this is what it looked like.
a 10 inch wide wheel is 11 inches lip to lip, and 4 inches of backspace means that the wheel has 11-4 =
7 inches of frontspace.
compare that to your 7 inch wide 4 inch backspace wheel, it will have 8-4 = 4 inches of frontspace. thats why wheels like this need a 2.5-3 inch spacer.
in the front I think that same truck had 15x8 with 4" backspace, which is 9-4 = 5 inches front space, and it looked great. it may need a 1" spacer in the rear because the fender spacing seems to be different front to rear on ADs, there is more width to the fender in the rear.