This is a good question... I'm beginning to think that you are on track with something as my tire/fender clearance is very minimal on my 69. I'm using year one 17" rally 2 wheels and have a hotchkis suspension (2"springs and control arms with stock hubs and brakes). My front end is tucked and love the look but it's a little too close for comfort. Last time I did the math I miscalculated my use of sold subframe bushings. The aluminum bushings reduce the body subframe clearance by 1/2 inch which calculates to a 1 inch tuck (approx). The problem with this is it reduces shock distance and I bottom out occasionally. The only thing that leads be to believe that they are the same is every vender says they work! Plus they have the photos backing it up.