We just installed the full/size red-top last week. Fits great. Comes with a hard plastic holder that substitutes for the stock one. Slightly different shape, more curved, snugs up better. While it's an excellent fit I can't advise on whether it'll hold up under autocross conditions.
My understanding is that there's a heat shield that needs to be removed -- it was already gone when we got the car.
Hope this helps.
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Steve, 87 Fiero GT, Getrag w/Ultimate Shift Kit, Street Dreams drop spindles, Poly mounts, KYBs, Michelin tires, Ocelot exhaust, Infinity audio, DashScan