You will definetly want to go with the 3 1/2" backspace over the 4". In addition to tie rod clearance issues, the 4" backspace will also allow the left wheel to contact the drag link on a left hand turn. Found that out the hard way. Had a customer that wanted a 15x7 wheel, which at the time was only available in a 4" backspace Japanese truck fitment, instead of the 15x8 Chevrolet 4x4 fitment that had the 3 1/2" backspace. While they did just barely clear the stock tie rods, the wheel did contact the drag link. I went with the 3 1/2" backspace wheel on my virtually identical truck (his was a shortbed, mine is a longbed), I have no clearance problems with either the tie rods or the drag link.
Wheel Viniques should be able to make the wheel with the 3 1/2 backspacing. We just installed a set of wheels from them on a '30 Model A that were custom ordered with a 15x5 up front with 2 1/2" backspace, and 15x10 on the rear with 3 1/2" backspace. They were the only company that would make that combnation, everyone else only had a 4" backspace with a 10" wheel, which would not fir without spacers. They quality was top notch, with very solid welds from the disk to the rim. Runout was very minimal, the wheels themselves were less than 1/4 ounce from true balance.
Last edited by LONGBOX55; 08/31/2011 2:45 AM.