I have heard that FC convertibles already have a factory brace in the location that Tanabe's Sustec Underbrace would go. Can anyone confirm or deny that? I want to get the brace and help my sloppy car if it doesnt have one. Here is a pic of the actual part.

 

Are you talking about the factory sway bars? The one on the back of the subframe. I havn't heard of the tanabe before but i have the Racing Beat front and rear. They considerably stiffin up the car.

http://racingbeat.com/FRmazda2.htm

 

The verts have a huge, heavy cross member under the bell housing area. Comparing to the piece in the pic, the tanabe piece is nothing. Anything you can do will help under there but unless you have a high mileage chassis and are running on the track I doubt you'll feel anything major. New bushings would give you more improved feel for the money.