The fat man axle design will require a much stiffer spring. Like twice as strong. It is because the axle is now a lever and the spring is only pushing on it about halfway out. Just a heads up that the spring pack will have to be twice the number of leaves.
Guy here in town did a Model a Ford with a twin I beam. Have no idea where he are the car are today. He drove it all over.
fyi...here's some more info on the fatman vintage IFS...shows an install: http://www.webrodder.com/article.php?AID=283&SID=16
The Jalopy Journal
