Not to sure what the differences between Z71 and ZR2, other than the fact that Z71 Came on the S-series pickups, and the Z71 came on the larger SUV's and pickups.
ZR2:
Ladder-type Frame with modified mounting points
100mm wider track (3.9 inches wider than regular S-10)
Increased ground clearance (Approx 3" over Regular S-Series 4x4)
Enhanced front (7.25" ring gear) and rear (8.5" ring gear) axles w/ 3.73:1 rear-axle ratio
Larger wheel and axle bearings
31 x 10.50" BFG A/T
Tires (Pickup), 31 x 10.50" BFG Longtrails (Blazer)
46mm gas pressurized Bilstein Monotube shocks
Rear track bar (pickup), front anti-sway bar (blazer)
Skid plates