IT"S a FORD where do I begin!
lol
Ok What kind of locker is it? ARE you sure you actually have what someone said they sold you? This usually the case on stuff like this.
Ford units look the same with out a trained eye open will; look like a posi and vise versa.
Do you have pictures of the rear diff you bought? will check it out.
Are your axles long enough to engage the clutch hub and the side gear on the driver side? This is another trouble area if you have a custom narrowed axle and axles.
Like I said...F O R D.... I have a head ache already.