I have a 66 fury 83/4 housing in my 64 300. The fury housing is about an inch or a little less wider than the 300-- Elmer, I assume you mean the center to center distance between the spring perches. Do you recall the overall (flange to flange) measurements ? I have several 64's and would like to do this swap and have looked at B-body rears as well as later model C-body rears and cant find one that will leave the tires where they belong in the wheel wheels. ie: bigger tires will clear the wheel wells with the stock 1964 rear but would put the tires into the metal with the wider, later model C-body stuff. Mike Laiserin