Thanks! the measurement is just what I need, the stock arm is 5.5" center post to center post. no flares but 275-60-15 TA's mounted on 15x10 Gassers W 4.5" backspace. Thinking the best is to get a another stock arm and cutting the length needed out of the center to make one.
That's what I plan on doing until I can afford to do a fiberglass gullwing from Kurk Collis. Just going to use two and have one made.
Got any pics of your van? I've been thinking about eventually switching from the 295/60s on mine to 275/60s.