Ok so it is 2.8 Liter V6 manual trans car, but we still need some more info. A Rattling noise usually doesn't indicate a serious engine problem, usually that would be described as a Knocking, slapping noise or possibly a ticking noise. Was the noise constant? Or did it vary with engine speed or MPH? Or even what gear the transmission was in? Did it vary with the clutch engaged or disengaged?
So when you try to start the engine, exactly what happens? Does the starter turn? And does it turn the engine over? Is there any unusual noise if the starter does turn over the engine? Did the engine overheat during the 20 mile drive.
What is the Oil level now? Low or High? Does it look like it has gas or coolant in it?
The reason I asked if the car was going forward or backing up when it stalled is there are only two things I can think of that would cause serious damage to an engine by doing Doughnuts.
1 - over reving the engine
2 - Some times at the end of the doughnut the car can momentarly be backing up, if this happens with the engine running, the transmission in a Fwd gear, and the clutch engaged it can cause the engine to suddenly try to reverse direction. This will cause it to stall, and possibly do serious damage.
I would start by draining the oil into a clean container and taking a look at it. Look for metallic flakes, or discoloring.
Fiero engines do not like to be run low on oil (this is more of concern for the 4 cylinder versions)
I would also see if you can turn the engine over by hand, usually by turning the bolt that holds the Harmonic balancer onto crankshaft.
More information is better than not enough in this case. It is very hard to tell whats going on with an engine over the internet!