Kevin isn't wanting to use the 12" rotors, just install the 88 front caliper with the 88 Fiero rotors.
The issue is caliper to knuckle interference when you have such a small rotor (10.43). The bracket above works with 12" rotors as the bolt holes are spaced a little more than 3/4" further apart.
On the 84-87s the 88 caliper body and the connection to to the knuckle are on the same side of the bracket (not the case for 88 brake kits), so the bolt tabs on the knuckle and the slider housing on the caliper must clear each other. You could try rotating the caliper vs. knuckle, but then you could run into interference between the caliper and upper a-arm.
[This message has been edited by fieroguru (edited 12-07-2019).]