Part numbers required for full retrofit to make the '90-'92 have the same braking system up front as '93-'96: (yes, even steel calipers) 
 

Parts I used: 
brackets & the air guides, then used 5/16" hardware for fastening. 

Note: the fender wells are the 'venturi panels' under the front of thecar. I opted not to purchase these, just use the air guides. 

The air guides attach to the front control arm & funnel air intothe rotor/caliper area for cooling.

(1.) Loosen the lug nuts onboth front wheels. After properly lifting the Z using a jack & jackstands (you will have to be under the car a little bit). Remove the frontwheels. Turn the steering wheel the appropriate direction to gain accessto the back side of the rotor shielding (backing plate 2.). Usinga die grinder with a cutting wheel on it, remove the lower portion of therotor shield. The metal removed should look like this. (3.) Takeextreme caution not to nick the rotor under the shield. A 1.5" cuttingwheel is required. After the shield is cut, you should end up with thewhole bottom of the rotor exposed. (4.) An extra hole is requiredfor fastening the plastic air guide to the end of the lower control arm.(5.) When the clamps (brackets) are tight, they only hold the guideto the front control arm, they don't get tight. The deflector counts onthis new hole to keep it in place in case it hits road debris. The clampsgo around the front control arm with the white dot toward the engine toaid in installation, the holes for the bolt are cut differently for eachside. Tighten the bolts down on both clamps, then bolt the deflector tothe lower control arm using the newly drilled hole. (6.) Put thewheels back on, lower the front end & tighten the lugs. You can seethat the deflector is fully exposed (7.)to air traveling under thecar. The 'venturi panels' would direct more air to the deflectors &install as part of the plastic shielding under the intercoolers.