Run the '90 rear, and get a u-bolt flip kit, or some u-bolts and plates from an f-150. Extend the e-brake cables and your done.
+ you get bigger rear brakes!
yeah, but what about the shock situation? stock shocks on a '79 are /\, '90 shocks are more are less straight up and down and one is on the front of the axle and the other is behind