If all you are looking for is the 12" C4 Rotors, the 88 Fieros are hands down a simpler upgrade.
On the 88's you just need the caliper bracket to shift the stock rotor outboard, the concentric rings and the bolts. Since the 88 calipers front/rear are essentially the same, you can use the same bracket Right & Left, Front and Back to lower the cost of the kit. This kit reuses the stock 88 calipers front/rear and parking brake and it is a bolt on swap that can be done in a couple of hours. The 88 upgrade uses 4 front rotors from an 88 C4 Corvette.
On the 84-87 to do the same requires purchasing a full set of 88 calipers, machining the front hubs to accept a slide on rotors, longer wheel studs in front, caliper brackets - which are different front/rear, the concentric rings are also different front/rear, then you have to figure out how to connect the 88 caliper parking brake to the 84-87 cables. The 84-87 uses either uses 4 - 88 C4 rotors or 1 set of fronts and 1 set of rears. The rear of the 84-87 must use a rear rotor from the C4 and using the front C4 rotor up front lessens the thickness of the needed spacer - so most current kits are based on the using front/rear C4 rotors. Overall this swap is A LOT more involved and higher cost.
If you start looking to swap over a different caliper (like the C4 calipers, then the upgrade on the 88 becomes slightly more complicated, but much, much simpler than the 84-87.
One of my old sayings was: buy an 88 and save $500 on your brake upgrade.
[This message has been edited by fieroguru (edited 04-29-2012).]
