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You want to read the RPO sticker to learn how your car is equipped. For an 85, if it is still in the car it is a White sticker located on the underside of the rear, left storage compartment cover (on the driver side) of the car.
If the sticker is gone, these pics are of the front spring, steering rack, and lower A-arms on my Original Owner, unmolested 1985 #26553 with Z51. If you car has similar identifiers, it is probably a Z51. Sway bar diameters are another clue to Z51 content. So are the wheel widths, if the wheels are original to the car, which 35 years later, they may not be.
This is likely the complete VIN for IHBD 1985 'if he posted correct last 5' - you can see the similarities of his/yours. You do need to ID components.
I'm not sure what the VIN of my car has to do with helping the OP figure out if his 85 is Z51-optioned or not, but if it will help, here is Dave's (WVZR-1) VIN for his 90: 1G1YZ23JXL5800653. How'd I do, Dave?