(I was just typing the same info when Gotemduster and Dartsun posted!)
It might be cheaper than replacing the wheels, but would there be enough room if you used a 3/4" offset kit for the leaf spring hangers It would require the spring pads to be cut & rewelded, adding labor costs.
I thought I heard that Cal-trac can make a "slightly" narrower spring. But I'm sure it wouldn't be enough by itself.
