Where art thou diff centres?

[rattlesnakehoey]

Greeetings Fordbarners, My stock flat 6, 3 on the tree (manual gearbox) propelled 49 Coupe pulls like a Trojan but revs too hard on the highway due to 3:7 to 1 rear end. I beleive that later '55-'55 Fordomatic Fords ran a 3:2 to 1 rear end. Where can I get hold of one? all leads appreciated. cheers from Downunder.

p.s. I have just checked over/detailed/ re installed eng/trans & would prefer to avoid the more complex route of replacing with overdrive box or Mustang, etc, rear.