I've lowered my '50 3100 3" on the rear and standard spindles on the front. (IFS bolt-on from Speedway). Speedway states that the IFS by design is 2-3 inches lower than original leaf springs.
Is there a site that will show you how your truck would look using different diameter wheels? I will either use 18" or 20" on the rear and 17" or 18" up front.