The spindles will give you as much as the spindles give. So a 2" drop spindle will be 2" lower.
My '69 was 4 bags, 8 valves, single comp, single tank, and 7 switches. I didn't notch the frame, but that would have gotten my truck about 3" or more in the back than this picture.
<edit> I had 2" (or 2.5?) drop spindles with front discs, also.