Will the hemisphere carrier out of a 78 series fit a 75 series?

Hi Aussie
Front diffs in the 78-79's are the high pinion as far as I know. A quick call to a wrecker will confirm if the rears are interchangeable in the front and rear of a 75. The axles may be different, the axle studs are larger than the 75's.
Cheers
Dave

No and no.

The 78 hemi has a different axle spline count to 75 and the ring gear is bolted to threaded holes in the 78, and straight holes in the 75 (bolt with nuts) They run different ratios dependant on motor.
Having said that....you can put the 78 complete diff centre/axles/brakes/wheels on a 75 housing if that housing is disc braked....
Andrew