8.75 rear diff,742 case,narrowed 3 in. HELP

The 3rd member is almost worth $800.00 , You should be running to buy it.

Truck Axles are fine re splined. They should be good for more power than you will be throwing at them. 4.30 is fine depending on how tall your tire is. May be a lil much on the street but who cares for the price. 742 Case is probably one of the strongest from Mopar. The pinion shaft does not taper. Spool on the street is fine as well. I run one without any problems whatsoever.