I am guessing you can use the radio from your blazer. I believe all you will need are 2 Scosche wiring adapters. One for your model 98 blazer and one for the Fiero. You then wire them together. Here is a wiring diagram

I chose the easy route and bought one off ebay. Cost about $15 more, but the wires were longer allowing easier installation and it came with the antenna adapter.
There are also posts here on the forum for installing a sub. Just don't have them handy.
[This message has been edited by sjmaye (edited 07-23-2007).]