4.11 are standard on all 1ks but the ute had the 4.44 so dont worry about finding one. Unless you cant find a 1200 diff or early pre 74 120y centre. Most 1k diffs have a bit of slack in them by now so most are a bit noisy. Best use a cut down pintara, late commercial van or other diff from live axle ute etc. However weight is the problem if its a race car. Im using an Alfa 105 gt diff which is lsd, all alloy and can handle the torque of a small block. Its best to use a diff from a sports car with live axle which has the lsd option centre from well known 3rd party companies. eg Mg.